The part numbers I provided above are Studebaker part numbers; they will work for SI and other Stude vendors, but nowhere else. Automotive body fasteners are often used only for automotive applications, so will probably not be available in small quantities anywhere except from Auveco. They do not sell retail, one must go through a dealer. However, you can drill down on their catalog to ID their part numbers. For example, here is their body bolt section. Bolts (auveco.com)