I was trying to figure out how to build one last year. They already have similar things for people missing a leg. My idea was to get one of those little snow blade things, and put a frame and seat on it with some pegs just above the ski. Think It would be nearly impossible to ride though. one other idea I had was to put to small ski at a 30-45 degree angle on each side, so when you lean to turn it touchs balances and helps you turn. mabye with a couple people working on ides we could get something that would work. Montana
USA founder Bill Jenack used to have one. He called it the Uni Ski. It consisted of a seat attached to a single ski (this was before snowboards). There was a picture in an old USA Newsletter of somebody (possibly Sem Abrahams) taking it down a hill. I don't know how it steered.
You could stick a seat on a snowboard, but it would be a variation on a snowboard and hardly a unicycle...
-- johnfoss
John Foss, the Uni-Cyclone "jfoss" at "unicycling.com" -- www.unicycling.com