Hi Setonix
You can get Impact ‘EiffelTower’ Cranks with 140mm length and they are on sale at Unicycle UK. Also you can get Nimbus VCX ISIS Cranks at 138mm length…
Here you go. I guess there is more available.
http://unaruota.com/ZC/index.php?main_page=product_info&cPath=14_17&products_id=719
And there’s also the KH 137mm!
Glad you tried that elPueblo! Doing so will also improve your technique in the longer run, so it’s all beneficial!
Just to clarify, I don’t think any particular length crank improves my technique. Rather, it’s the experimentation with different sizes I think has helped.
I have not made up my mind which is better. I am a little concerned that the 150mm cranks could be harder on my knees and the tendons in my ankles in the long run. Some riders have associated knee pain with excessive motion, which can result from longer cranks, but my concern with smaller cranks involves the physical strain on the knees.
The 150mm cranks I’m using are Ventures, with almost zero Q-factor. I have read many, many threads where Q was discussed, but I’m still left wondering what is ideal. To boil down the Q-factor wisdom I’ve received: Low Q is better for cadence, while high Q is better for maneuverability and side to side balance. But, when one or both hands are responsible, in part, for steering the uni, how much maneuverability is needed from the feet?
For a considerable time, I had higher-Q cranks on my muni. Then I bought a new pair of Venture 165mm and installed those. On my first ride, I kept inadvertently stepping on the cranks. But then I adjusted, and that was no longer a problem. What that suggested, however, was that my feet may have been hugging the cranks on the higher-Q cranks. Because of the outward bend in the high-Q cranks, though, there was no stepping on those cranks. So, I wondered if, maybe, lower-Q cranks were right for me, because already my feet tended to push toward the inside. I never felt, even while using smooth pedals, that my feet were migrating outward from the pedals. It was more the opposite in my case. So, maybe the correct Q is whatever is natural. If someone could invent an extra large, smooth platform pedal, then the foot could be allowed to find it’s natural position while pedaling, maybe that’d indicate the correct Q-factor.
I can’t remember who posted it but there is a picture floating around somewhere showing how if your feet are too far apart your knees point in, and if they are too close together your knees point out. If you find a width where your knees are neutral that’s probably the right width for you regardless of the type of unicycle or bike.
Update, I took a 12 mile muni ride with 150mm cranks on my 26" (comparing them to the 165mm cranks I’m used to). There was one hill I wasn’t able to make it up, which I can do on the 165s, but which I almost made it on the 3rd try on the 150s. The local high school’s cross country runners call this hill “the wall”, because it looks vertical when you approach it from either side. So, I think it’s doable on the 150s, but the technique I used to climb was more of the weight-shifting-dance variety. Climbing the steep hills generally took more energy, and by the end, I felt like I was really slogging them. However, when the ride was over, I felt more fresh than normal.
I think it’s a combination of those two. Orthopedically, we are all a little different. Just as we have different seat preferences based on differences in our crotches. I think some people naturally walk with their toes pointed outward, and others pointed a little inward. Mine seem to point a little inward, so I generally do well with flat/low-Q cranks. So I think the “foot pointing” (I’m sure there’s a word for that) and natural knee angle are both components in how we fit our unicycles.
For what it’s worth (our bones, joints and tendons are different), My Wilder Muni originally came with 170s. That was when people were using really long cranks to try to ride up everything. But long cranks are slow cranks, so then I got a pair of 160s. Those were better, but then I was getting passed by people on 26" wheels. Young people. So I eventually notched it down to the next smaller size from Profile, which was 145. Those were definitely on the short side, especially for going down steep stuff (I have stories), but mostly they were great. I would have added a brake to that uni but there was no way to do it without welding to the handmade aluminum frame, so I never did. I rode with those 145s for many years.
In recent years, the vast majority of my riding was on that, and my geared 36" with 150s. I even lost my “speed legs” for Track racing (which uses 125 cranks). When I recently switched to the 127 holes on my newer KH Muni, I had a blast on the flats and downhills! Later, I was amazed that I could ride up a lot of stuff, but not as much as with the 150s of course.
What I’m getting to is, I think you will do very well with the 150s, so give them some more time, and monitor your joints to make sure they aren’t being negatively affected. You still have lots of power with that size on a Muni wheel, and should be able to climb up all sorts of things with practice. 
Do you mean to say with this that whatever crank size, you are bound to get knee pains? For me the nuisance started after taking my 19" on a 10km ride. Just in the period where I was learning to hop, which doesn’t do much good on my knee either. I still think with my 29" Nimbus with 150mm cranks and the seat not too low, I have limited pressure on the knees. Also I have no probs riding the 32" with 150mm cranks. After such a ride I only have saddle aches
I think my prob with the knee pain is that somehow I twist my knee during a full rotation. I’ve started again with going to fitness 2 weeks ago (3x a week) and putting focus on leg training, so hopefully my knee pain will go away at some point.
I reckon the good side of it being dark and cold when I come home from work is that I don’t ride as much as I would in spring and summer, so my knees get more rest.