The one you just missed at CM and one at Boyne last week (Burton, K2 and Rome)... then there's the Burton one at Boyne in February... unfortunately that's all that I really hear about in MI. There's a huge demo/trade show the week prior to this Burton thing in February but it's industry/invite only.
Marhar Snowboards out of Grand Rapids will probably do a few demo days (just them) at Cannonsburg and Caberfae. They might make it back to Mt. Holly later in the winter like they did last year, too. I haven't heard anything definitive yet but I'd be surprised if they don't do at least a few.
The only other company aside from Marhar (which is local) and Burton (which is huge) that puts much presence around MI resorts is Rome but I don't think they do any demos, mostly they just sponsor rail jams and other events.
Any particular boards you're interested in, or did you just want to get a chance to try out as many as you can?