I work for the DEP in CT and trust me there are no legal PUBLIC riding areas. There was a place in Meriden called Higby Hollow but was closed by the town.
I also have owned a few quads a polaris 99 400 scrambler 4x4 and a 94 honda four trax 300 4x4, but was limited to riding them in the woods behind my parents house (only about 10 acres).
The thomaston damn is not a legal quad area, you can only ride dirt bikes there.
The only 2 suggestions that I can think of are to find a friend who lives in mass, nh, me, or ny, where quads are allowed to be riden legally, or become a part of an atv club that either has land donations for them to ride on, or takes trips north to legal riding areas.
I know this sucks horribly but there's nothing to be done about it.
I have looked into the problem quite extensivly talking with CT foresters and Conservation Officers and the problem is the lack of any sizable piece of land. In order to be able to open a public place to ride there has to be a conciderable amount of land, or people would be on top of each other, and something that large is usually already being used as a State Park. CT just doesn't have enough open space to obtain a large unused piece of land.
Good luck finding some places to ride. Hope you do better than I could.