If you go to the National, 707 will have a large table there and you will likely see more 52 Mantles there than all the other tables combined. Levi Bleam, the owner, will be wearing a large and ugly top hat. He is the most knowledgeable person on the planet about the 52 Mantle. His prices tend to be high but he sells only the real deal. He is friendly and if you tell him about your quest he may have some insights for you. I got both of mine through him, one of each "version" as Adrian put it. It, along with the Thompson and Robinson, was a double printed card on the same sheet and has subtle differences on the front and back
