Summarize the following:
However, as explained in the section on buying at flea markets from an unlicensed dealer, you run the same risk of buying a stolen firearm and having to surrender it with no compensation.  Private sales are a great resource for finding antique firearms. As a rule, they will be priced considerably lower than what you will find in an antique store. In general, be leery of the "fantastic deal" offered to you by a stranger. Ask if the seller will allow you to pay for a licensed dealer to handle the transaction through their store. This will allow you to have the serial number checked and give you peace of mind for a relatively small transaction fee.

Summary:
Search the "For Sale" ads online and in your newspapers.