I think the 36 is a standard for unicycles, so rims, tyres and tubes already exist, you just need to lace it up to a hub
I was curious so I did a search. I found a Nimbus 36" for $900.
Giant also makes one. Also found a Truebike with a typical Chinese translation for the description. It claims that with the standard gears, " acceleration is higher because one pedal revolution covered longer distance of the bicycle." I would have thought acceleration would be slower, not higher. And $4,440?
https://www.truebikes.eu/
Overall, it seems that most unicycles range from 16" to 24". I also saw mention of an electric unicycle, but you stand on it. The bike world is an interesting place.