Chicago mountainboarding organizations eh? Well I found a website for chicago land kiteboarders, if you check the forum http://www.chicagokitesurfing.com/kiteboarding_messageboard/ I'm sure you'll find some kite atb'ers that mountainboard.
Other than that I know there is an extreme sports park in joliet, which may be your next best bet. http://www.cpxsports.com/
Are you wanting to set up an event of some sort? Its good to see interest in promoting this great sport.
