In the early 70s, John W. Caler Books advertised in Air Progress magazine, and I bought some from the enterprise. The company started a book club with the promise that all who signed up would receive a piece of a Messerschmitt 109. (Bf or Me, they’re still 109s) I signed up, received a few lists of books for sale and bought a few more, including some German language reprint, reduced in size, of 109G maintenance manuals, well illustrated. They’re still in the AeroKnow collection. I was satisfied with the piece of the 109 and will someday display the card with a late-model (probably 109G from Hasegawa) 1/48 machine.
I lost touch with the Caler operation. Perhaps they folded. If you know what happened to the businesses or 109, please update in the comments.