Are there any gun shows coming to your area? They can be a source, as ammo collectors are usually there also. Some of the gun papers on the market often carry ads from people in this line (Gun List, etc.).
Do you have any local small papers in your area, such as trader's guides and such? It usually doesn't cost much to run an ad in them, and you never know what you may find. Just a few suggestions, and wish you good luck. Perhaps some of the other good people on here can help-----