In the South East & the CenDiv there is a IT7 class which is X ITA 1st gen cars. There is also a seven race series at Mid Ohio. Do a search on this site CenDiv page.
First you gotta find a few 3rd gen race cars, since they're only classed in GT2/3, with non turbo motors. I hear there's one in So Cal, haven't seen one up here in NorCal.