Just spotted this on Wiggle in the UK.
Meant for a bike, but could be suitable for 1 or 2 unis depending on size, although I have not checked out the dimensions.
I’m going to give my 2 cents on this topic since I recently traveled with my unicycle across the US to attend the Brooklyn Bridge ride and NYC Unicycle Festival.
I’ve only been riding for just over three months and have a 24" Sun Classic unicycle. I really wanted to participate in the Brooklyn Bridge ride and had to figure out a way to get my unicycle to New York via airplane. I search google and this website for advice and came up with the following solution with inspiration from Adventure Unicyclist.
I went to my LBS and asked if they had any left over boxes and packing material they could give me. I ended up with two very useful boxes. The first one was a box that had contained a mountain bike wheel set. I took the pedals and seat post off my uni and it fit perfectly into that box. The wheel set box didn’t seem strong enough to endure the trip so I then took a bike box that was slightly wider than the wheel set box and cut it down so that the wheel set box would fit in the downsized bike box. I then measured the outer box which turned out to be 24" x 30.5" x 7.5" (62 linear square inches total) and created a bag to fit over the box. The bag is a simple rectangle made out of 1000 Cordura fabric with a zipper on the top and the corners tucked in. I put my seat, pedals and tools in with the uni and filled the gaps with bubble wrap that the LBS was going to throw away. Material, webbing and a zipper for the bag ran around $50.
The unicycle made it to New York and back via the Newark and Seattle airports. I had no problem checking the bag for the flights. I got absolutely no flak from the agents at Alaska Airlines. Even though it was within the allowed checked baggage dimensions they did have me take it over to the oversized check-in counter in Seattle. When it arrived in Newark it came down the regular baggage chute. Hey, I even fessed up when the agent asked me what was in the bag. I just said, “a unicycle”.
The whole package weighed 22 pounds. It’s not the easiest piece of luggage to carry around but it wasn’t too bad. I did have carry it up and down a few flights of stairs to catch a bus when the AirTrain at Newark stopped working but that was manageable. I added some D rings on the side so I can clip on a side strap if needed.
Ok, I’ll admit this is probably a lot of trouble for a Sun uni. I looked into buying or renting one in NYC but didn’t come up with anything. Really the only option was to bring it along on the plane with the chance that it might not make it there and back. No biggie for this wheel. If it didn’t make it then that meant I could buy another better uni!
There was another thread about carrying bags for unis.
There is lot of pics showing all the ideas tested. I posted my version on page 2. It is along the line of the OP but simpler: a mountain bike wheel bag ($30) and some pieces of cardboard and the parts & clothes (are doing a final padding even though it is already plenty strong without padding).
Did a round-trip US-Mauritius and everything went well. Requires to remove pedals, saddle/seatpost & deflate tire but that remains manageable 
Siddhartha I read that thread and many others. I looked for the bag you use online and couldn’t find dimensions so I didn’t buy it. My LBS didn’t have anything like it.
Many of the threads had links but none had a viable option for something I was sure would work. I could have gotten the one from UDC but I didn’t like the size. The O’ Some bags look great but UDC (US) doesn’t sell them.
I’ll probably make another version for bus/train travel.
My mom made me a big square bag for my uni. I can only bring one uni in it, but since the bag is pretty small, it’s awesome for traveling light. It’s 30x30", it has a handle and a super heavy duty zipper on the top. It fits up to a 27.5" wheel with clothing! The really cool thing with this bag is that once I get to destination, I can build up my uni, roll my bag and strap it on my backpack! I’ll try to find a picture very soon. I think it’s the coolest setup I’ve had for travelling! 
Thanks mom!
I recently flew from L.A. to Seattle with my 24" Torker. I bought a 27"x27"x27" box (less than $10) and cut it down to 8" tall. I used the extra cardboard to pad the inside of the box. I took the pedals and seat off, and had room in the box for the unicycle, pads, extra clothes, extra shoes (basically all of my luggage except for carry-on). I put some nylon straps around the outside for extra support, and also to make it easier to carry.
I spent a month in the US this summer and had a big suitcase for that matter. I would have loved to take a bigger wheel, but in the end only my 20" (deflating the tire) fitted in it – though still requiring dismantling. I could probably have been able to fit a 24", but it would have required removing the tire and placing it diagonally in the suitcase, making it complicated to arrange clothes and stuff around it.
Having said that, I’m glad I did it because I rediscovered my 20". I had mainly used it inside (freestyle uni), but outside with 100mm cranks and a slightly lowered seat, it proved to be much fun around Brooklyn.
I already posted HERE my awesome home made unibag for 20".
Now I bought and tested bag for 24-29" uni.
After some researches I found Continental double wheel bag at CRC and according to comments it can fit 29" wheel with tire. I decided give it a try due to flight to Vyborg outdoor fest in Russia.
24" MUni fits perfectly in one pocket and frame w/saddle putted in backpack + safety gear + tools in another pocket. Weight was about 12Kg. Shoulder strap gave chance to carry it with back pack on.
Also I tried to put 29" wheel w/2.35 tire on and it also fits perfectly.
Nice bag 
29er:
In airport w/24er inside (zippers locked with zip ties):
Hi Cavernap!
I remember you mentioned putting your uni in a box which gave me the idea of putting mine in one. It was nice not to have do much to put the uni together. I’m definitely know little about putting a uni together once it’s stripped down. I was concerned I would mess up the hub. Hopefully I’ll learn more in the future.
Hope you make it back up here sometime! I’m now riding around Green Lake which has a three mile loop. Maybe if you come back up and the weather is good we could meet up there.
Melinda
I will definitely be returning to Seattle with my unicycle! I had a great time, and found lots of fun places to ride. I have been riding at the Rosebowl that has a 3 mile loop, but lately it has been too hot. So instead, I have been concentrating on free-mounting, but not doing very well. Vertigo–I like your mantra about lifting the back knee–that seems to keep my weight off the pedal. But I can’t seem to jump high/far enough with the other foot to get going. And if I concentrate too hard on jumping, I forget to unweight the back foot. Argh! How are your freemounts coming along?
Keep up the practice. Hope the weather starts cooling off down there.
My freemounts need work but at least I can get around with out something to lean on. Usually takes a few tries. I get on top and then don’t lean forward or I put just a little too much weight on the first foot. Actually my UPD rate had gone way down so I have less freemounts to do.
I have a lot more incentive to save a wobble when I know I’ll have to freemount if I fall off!
Is that the road version? Did you check the bag or carry on?
When I traveled to New York for the Brooklyn bridge ride I took my 36" uni in a soft rooftop car carrier. The bag was great because I could carry all my riding gear and tools. However, I had to use four straps to snug it up because the bag was large. I flew from Chicago to New York round trip on United Airlines and both times security checked my bag. They didn’t care much about repacking my bag.
Cost for an oversized bag to New York was $25.00 and back to Chicago was $150.00. Both airports were confused about an oversized bag. Next time I will do my homework or just mail my unicycle to my hotel.
From your description it sounds like a 26 inch fattie would fit also?
Would a 26 fattie and a 29 road wheel fit?
With only a 26 fattie would the frame and seat post fit in the second pocket?
Thanks.
Reid
I was able to get a 26 in a duffle bag with all my stuff staying under the oversized limit for Unipal. I just had to take the tire off the rim to make it fit.
I’ve found several suggestions in various threads on this topic but most don’t list specific details such as dimensions or brand/model. The wheel bag looks promising. There are two versions offered. Seems like the mountain bike version is for a 26er and the road version is for a 29er but I’m not quite sure. I’m looking at options for my 29er with Big Apple tire. I’d prefer to keep some air in the tire. It would be great if I could take two wheels. I’m also considering the bag that John Foss suggests. I’m just a bit concerned whether it would protect my rotor from damage.
I’ve made several trips with my 24" or 26" unicycle in a cordura bag that covers a corrugated box ( 24" x 30.5" x 7.5"). To get the 26" wheel in the bag/box I had to take the frame off and deflate the tire. I taped the road tire to the rim hoping that would give the rim some protection. I also folded the muni tire and put it in the bag with the wheel. The 26" frame traveled in a separate suitcase. I haven’t tried to get both wheels in the same box. I doubt they would fit. I think my box in a bag solution gives the wheel a lot of protection but can be a pita to carry around especially if train transfers are involved.