If you are in the Eastern PA area in mid September, think about swinging by the Lehigh Valley Postcard show. Not sure what to tell you to expect as I have yet to go to one.
On a side note, my Mom bought me a big box of vintage postcards, most pristine per her on the longest garage sale. Last year she got me a typewriter. Apparently this box went on sale for $10. I have yet to see the contents, but expect some sharing when I do!