Hi
I was thinking of doing exactly the same thing a few weeks ago (UDC UK had Hatchet frames but no complete hatchet unicycle at that time) and I spent a bit of time looking for 36 hole rims. Things seem to have definitely moved to 32 hole.
I ended up on St John Street Cycles website, where they have a bit of choice of 36 hole rims for both 26" and 650B. I didn’t look at what widths of tyres you’d get away with on any of these rims.
There are some Mavic and DT-Swiss rims there and stuff at various price points. Interestingly I spoke to a guy from DT-Swiss on a trade stand at the Fort William MTB World Cup Downhill at the beginning of June and he said they didn’t do any 36 hole rims. In the end I was thinking that I might just go with a Dominator 2 rim.
I haven’t actually done anything about this yet, I stalled on it when I saw they had fully built Hatchets in stock, but I didn’t really want to spend that amount of money.