It all depends on what you need and what you're trying to do. As far as aftermarket interior parts, you can usually find window cranks, door handles, carpet, and dash covers on eBay. There is also a company that offers just about all the upholstery materials with which to have your seats done. Other than that, if you're staying with a stock look, you pretty much have to source used parts, but there are vendors who are quite good at that. If you're into customization, there are more choices. You might try looking at eBay under Ford Pinto NOS, where you'll find a decent selection of things. Hope this helps. Good luck!
Dwayne