Wild Guess: No such thing as "new" seat covers. I bet GM discontinued them years and years ago. Too many varieties--colors, patterns, textures, seat shapes--for the aftermarket to deal with. Call your local gm dealer and see.
The maroon leather driver's seat cover of my '97 K2500 had a HUGE hole in the seat bottom. Typical slide-into-the-seat-with-tools-in-your-ass-pocket wear. The seam between the seat and the side pieces was still intact, but the material on either side of the sewn seam had holes big enough to push a cat through. Leather on the seat, leather or maybe vinyl (advertised as "Leather seating surfaces"--but the sides and rear of the seatback may not be leather) on the side panel, color matched.
I removed the seat (rusted bolts, broke two of the four, had to drill the broken pieces out of the weld nuts, then re-thread the reinforcement (welded nut) in the floorpan.)
Hauled it to the local auto upholstery shop in the early afternoon, had it back by the next day. They'd inspected it previously and ordered new leather in matching color, so they were ready to go when I showed up with the seat.
They built-up the sun-damaged foam while they were in there. I can't tell it was ever damaged except for a couple of spot-repairs they made in a third leather panel that had minimal damage--too minor to replace the entire panel. The color match was exact on the new material, the texture on the spot repairs isn't perfect...but overall it's a thousand times better than it was.
I think it cost me $150-ish. It would have been higher if they'd had to charge billable hours for dicking with the rusted bolts.