Brutus,
If by later model you mean 80's I may be able to help. As you know mine's a 74 with 82 seats but you may not know (and that's a big call you know most else), the 82 seats are taller then pre 80's. In order to fit them to mine, the floor pan had to be dropped an inch and a half.
As for availability, unless you can pick them up locally, I'd suggest the best value place to get them from would be J&D Corvettes. They'd have them second hand in pretty good condition and I'd say you're planning to re upholster anyway so color won't matter.
Good luck!