I don’t think that there are currently any companies making a quality 22" unicycle.
I think that Koxx-1 made some a few years ago but I doubt there were many sold.
I think your best bet is to put one together from pieces. You won’t have any problems using a 22" wheel in a 24" frame, the crown will just be a bit higher than necessary. The 2007 KH20 frames had a pretty high crown so I think one of those might work for a 22" wheel but I would want measurements of the actual wheel diameter and the frame axle to bottom of the crown before spending money.
found the thread with a guy selling 22" rims and tires