In Colorado I'd think a solid 200+... but many are really just water kiters who dabble.
In the Elks, I think there are a dozen or so part timers. There are more in the Eagle valley - summit county: but probably less than 100. Not sure about the Boulder/Denver area but surely more than 100
Thanks Catsh16, that's useful info for me. Basically all kiters are kitesurfers for that season and snowkite if they live in a favorable snowkite part of the continent during the winter. However, there's more snowkiting going on out there than I originally thought. I have to give a talk on the state of the industry at the Summit coming up, that Colorado info is helpful!
Here in Wisconsin the winters are highly variable. Some years we get lots of snow and cold (like this one), and some winters we get only a few weeks where the snow/ice conditions can work (like last winter). I've snow kited more this winter already than I did all last year. Still not up to 10, but getting there fast. I also have snowkite-specific gear (snowboard with a switchblade adapter). Most of us ride most of the time on frozen lakes. It's unusual to get enough snow to cover the terrain enough to ride on land, and the land is all privately owned. Most of us haven't taken the time to try and get permission to ride on private land because the conditions happen so infrequently.
I think way more than half of the water kiters here also kite on the snow/ice. I know of only one snowkiter that doesn't kite on water. I'd guess that in Wisconsin there are probably 50 - 100 kiters that will get out on the snow any time the conditions and their schedule allow. Maybe it's only about 42.