My last set of 15’s were Firestone Indy 500’s. They were significantly better than the T/A’s. Their discontinuance was the major reason that I switched to 17” wheels as I did not want to go back to T/A’s.
15” tire choices are very limited these days.
COOPER COBRAS seem to be appearing everywhere..
The classic BFG RADIALS T/As are experiencing a brown lettering issue so lots of people have moved-on to other brands.
As much as I love the 15” rally wheel look on my ‘75 I moved to 17” wheels 15+ years ago.
This gave me a lot more choices for performance tires as I often Autocross the car.
Are you looking for any tire or more like original from GM? If you want the original type tires that came on the car new, Kelsey tire sells the original GoodYear Eagle GT tires. They are pricey, but I always run them and like the tires. GY Eagle GT