BLC,
Welcome! Repro seat covers are available from the two most common stovebolt suppliers, Chevs of the 40s, and Jim Carter Chevy. Check in the links.
That being said, the material I got from them is not rare. Seats were either brown or Black, not complicated. The replacement seat covers I got were not EXACTLY like the originals (seem in the middle of the riser, straight-cut corners instead of the "curved" insets of the seat cushion.)
I took the original seat cover to a local auto top and upholstery shop, along with the repro. $115.00 to match the material ("Ox hide" was the texture, I think . . . ) and cut it to the original seat pattern. I thought it was pretty reasonable. Pickin' it up tomorrow morning.
Why not give local a try?
Just an idea . . .
-Michael