Depends somewhat on how accurate/original you're looking for. I prefer to use the fasteners off the car. I've had member Eric Manuel ("3404") do my plating on several cars, and he was reasonable, prompt, and got the finishes right.
Note the markings on the bolt heads when comparing to a kit. You can also try AuVeCo or similar fastener companies.
I've bought interior-screw kits before, but many of the screws had incorrect head sizes: Chrysler used a lot of #8 screws with #6 heads on them.