Very interesting find! There's only one snowboarding game on the Dreamcast, Rippin' Riders
, and the boards in the game were made by Salomon; so if they were to make a promotional snowboard for the game, it would have been made by them, not Elan. There was also snowboarding in Xtreme Sports but it's only a small portion of the game and there's no branding at all used on the snowboards. So yeah, I doubt it was a promotional item for a particular game. Plus it would likely have the game's logo on the board if that were the case. In summary, where it came from I have no idea. lol It's a strange promo item to make if your not promoting a snowboarding game. It's possible that someone that was a big Dreamcast fan just had it custom made but that's just a wild guess.
Maybe you should try contacting Elan
. They could probably tell you where it came from (assuming it's not custom).