Amped up racing series based in Nashville races mainly LO206, I think they have a shifter class, not sure what turn out is like in either class but I don’t think they run TAG.
Check out Atlanta Motorsports Park in Dawsonville, GA. It’s about 2 hrs drive from me in Chattanooga, short enough to make a day trip. I started racing there last winter. Great track, races once a month, good TAG fields and shifters most events. There is a facebook group and they guys are pretty good about letting the group know ahead of time if there will be enough shifters to make a race.