There's a small one in Lancaster MA, not sure what's going on out back of Rye Airfield at the moment, but they were working one there too, the Littleton track and jumps are gone, but will be rebuilt at some point. Cutler park had a little one, not sure if current status.
There's a few in NH, one in the Keene area I think, but could be wrong, that's on private land but open to the public. Bretton Woods has one too.

Kingdom trails of course, and Johnson VT has a public track and DJs. There are a hanful of others around - do a google search and you can check out vids, etc.