When I'm searching for particular fabric, I may start the search a couple of years before the project. It can take that long to find the right things if it isn't currently commercially available. For what is commercially available, this search from fabric.com pretty well shows what's out there:
https://www.fabric.com/find?fiber-co...searchText=car
I've used the major sites for re-sellers, first I start out at Amazon, and yes I look at ebay and etsy. For the most part, I haven't had any problems in 20 years of buying from individuals or small non-local businesses on line. I've had many problems with the chains over the same 20 years.
In this case, going through Spoonflower yourself or others is probably the way to go. Lots of things under cars, here's a search on mustang which means you have to go through some horse prints too:
https://www.spoonflower.com/en/shop?...rt=bestSelling