Great thread and photos!
I am guessing that the interior on my 1979 CVX-18 was redone, and the vinyl is a little lighter than the beige color Hyperacme posted on 8/22 at 12:04:02 (the 3 photos with the life jackets between the front seats).
I got a couple of vinyl samples in the mail from a seat manufacturer in Indiana, Veada:
https://veada.com/The sample that most closely matches my seats is labeled "Alpha Marq. Milkweed."
It does not sound like they do custom seats, but I might order the vinyl from them.