I have several cameras (Including my M6) who don't have memo holders. I have forgotten if or what film is in a camera at least once so I felt that one of these was in order.
I couldn't find them on the 'net, so I modeled a few up and had them 3D printed. I'm bonding it on with 3M body molding adhesive. Very strong but will come off if necessary.
Works like a charm. Shot #1: The memo holder mounted Shot #2: The tape ready to mount.