Check out :
USASA: United States of America Snowboard Association - New Hampshire Series Information
USASA: United States of America Snowboard Association - Maine Mountain Series Information
USASA: United States of America Snowboard Association - Massachusetts Series Information
Depending on where you are in NH those three USASA regions would work for you. I know the guy that runs the Massachusetts region and coached a freestyle team in Western MA. They were always really good events, lots of fun, good competitors and they give away tons of free stuff after every event.
As far as coaching, I can't help too much though lots of mountains have freestyle specific season long programs which could help, though that's different than actual coaching. I would poke around the usasa website and maybe email the director of whichever region you want to compete in and maybe he can put you in touch?