For restoration and repair of old vehicles, Ebay is oftentimes your best bet.
More and more salvage yards for cars, farm implements, motorcycles, snowmobiles, etc... are listing at least partial inventories there. If you don't find the specific part you're looking for, but find parts for the vehicle you're working on, it can give you a lead to reach out to the seller and ask if they have the specific part you want, but haven't listed it.