Welcome to FABO! Your local auto dismantler would be the fastest, easiest, and probably cheapest. If you don't have one nearby, having them shipped in would be the next easiest but might take a bit longer to get. The studs should be available new at your local hardware store or NAPA auto parts supplier. I have some used ones but maybe another member here is closer to you? How many of each do you need?
Thanks, Mark