Dxers will enjoy this I'm sure. This ex radio engineer from Montana has a collection of reply cards that goes back to the early 1960's ranging across the U.S. and includes more than a few from Canada and Mexico(towards the end of the scroll). As well, he has a number of excellent vintage color pictures of radio station buildings, studios and towers located on other pages of his site. I hope to post some of these here but,am awaiting an email reply from him in order to gain his permission to reproduce them. In the meantime, I'm certain he wouldn't mind your visit and exploration of the site.
http://www.johninmontana.com/dx/qslcards.htm