I don't think there is a market for 100% original race drivin's, and I don't think the Smithstonian will give a shit in 20 years, so just put something on there that you like.
Put some sweet yellow stuff on there or something.
Anyways, you need to go to a fabric store and look in the upholstry sections.
I just used a cheap car mat from Wal Mart, just had to cut it to size. I had some spare carpet padding that I put underneath, so it's actually comfortable.