Carl,
I have a lady friend that is into vintage tin and ceramic signs, as well as tin containers of all types. Antique stores, flea markets, ...etc and of course eBay. Sometimes you can actually con a real station owner into parting with one. The original vintage signs will carry a sizeable premium, especially signs dealing with petrolium products, gas stations, ...etc. The same with vintage tin cans. The gas product stuff is highly collectible now. Be patient, there are still good pieces available, but beware of the repro's. If the signs look too good, they're usually fakes. Most of these types of signs rarely are in mint condition since they were almost always outdoors and should show weathering.
Good luck in your search. Just this holiday I found her a Sunoco Bicycle tire patch kit tin container in "good" condition and paid through the nose for it. But if vintage is what you want, pay you usually will.
Regards.............. Bob