For sure! I've been meaning to prepare a proper guide for community promotion (as have a few other cool users).
First step would be to regularly post in the community. If you have other snowboarding feeds, news, blogs that you follow, just repost the cool things that you see. Photos of gear, memes, any (good quality) content really. A lot of people interact to communities from the ALL feed, and many may subscribe for more.
Finally, you can name-drop the communities in relevant threads as appropriate. If you find that the first step isn't working well, you can also crosspost from the snowboard community to other relevant communities (ex. a nice mountain photo to !pics)