I found a company that's willing to reproduce the pattern/texture of the vinyl seat fabric for my '73 510. I'm pretty sure the pattern/texture of the '73 is different than earlier years. He's quoted me approx. $100/yard. I'm guessing 3 or 4 yards for the 510. This seems reasonable considering he has to make some expensive tooling. He currently reproduces a lot of other vinyl patterns (mostly American cars), and owns the equipment to do it. Basically the vinyl, under heat and pressure, is embossed/pressed with a roller that has the texture in it. Easier said than done.
The initial run for me would be black, but I assume any color can be done. I'm pretty sure the '73 came stock with either white or brown. I'm converting mine to black.
Is anyone else interested? The more people, the lower the $$.
Here are pics of what the pattern looks like on my '73 seats: