I used to mix in some Sunoco 260 GTX, 98 octane, just for peace of mind. Once I finally got some good track day logging done, I realized I didn't need to. My car is still NA, though.
I got the gas from a station out in St. Mary's. Can't remember the name. You can go to
www.racegas.com/fuelfinder to find your closest station/dealer of the Sunoco fuels.