Well, I seem to have found an answer to my own question, a No-Fog breath deflector (
www.nofogusa.com). At about $40.00 delivered it ain't cheap, and adjusting it to best effect is a bit fussy, but it WORKS. It's made in the USA, seems to have a big following among snowmobilers, and they actually answered a Sunday afternoon email with a Sunday evening phone call when I had a pre-order question. My cold-day rides are now considerably less thrilling, but that's a good thing.