Are old postmarked postcards some over 75 years old sellable and whom should be contacted?

Yes your old postcards are sellable. You can do it one of a few ways. Take to an antique store and see if they want to buy them. Museums are also a good place. My husband has purchased some off of e-bay as an addition to his collection of old military memorabilia. Hope this helps.

Some collectors look for the actual cancellation mark instead of the postcard image. Most rural post offices and train stations no longer exist.