Are you looking for modern seat upgrades? If you have a good wrecker near by, take measurements of your seats and pics of the tracks to compare. Another upgrade people have done is add cup holders in the console. Also what colour interior?
A lot of vintage upholstery is still available from certain vendors and shops. Amazingly, certain older and more unusual colors/patterns seem even more available, because no one else is using them up. A shop I use was able to get original 1970 Cadillac fabric recently. I'm guessing there are tons of various '80s GM materials available.