Not sure what you mean by seat covers if you are referring to original pallex material the grey and black none of the reproductions that I know of are exact like the real stuff.
I have original dated C & A grey pallex material C & A is Collins and Aikman that was the supplier of the pallex material for Buick. I may be getting some black in.
I have sections of it.. its not cheap.
Otherwise other companies do sell the reproductions already made up. which would be cheaper. The real stuff that I got runs about $165 per yard.
If you are looking for a decent seat cover, have a look at these. I have a set, and they work well, plus they are easy to remove at a show or cruise if you want your original seats to show.