The walls in my office have grooves built in for hanging chalkboards, and I see that one chalkboard in the office has already been hung using a mount composed of a spring, a metal piece, and a screw (see photos). The way it works: the metal piece and spring go into the groove. The metal piece is rotated to hold onto lips of the groove, and the spring makes sure that the metal piece stays flush against the lips (rather than wobbling inside).
I'd like to get more of these mounts (the item in the first photo) to hang more boards, but I do not know what it is called, or if it is even commercially available. I have also never seen grooves like this built into a wall, but this is an old university building. Any help would be appreciated!