After years of looking for a mirror adapter that was cosmetically and functional mint, I succeeded in finding one.  They're unusual and often not in good condition.  The one I found may be missing the rear cap (if there was one), box and instructions,  But it's in great shape.  Here is what Asahi Optical Company had to say about the accessory in various publications from 1972 - 1976:

An interesting adapter for detective photographers, this allows you to take photographs by NOT pointing your camera and lens to your subjects. Fits the Takumar 200mm f/3.5, Super-Takumar or SMC Takumar 200mm f/4 and Tele-Takumar 300mm f/6.3 lenses only (From Spotmatic II Manual, ~1972)

Right Angle Mirror Adapter. Fits telephoto lenses having 58mm filter diameters. Cat. No. 7096 . $118.00 (from Honeywell Pentax Cameras Lenses and Accessories, Nov 1973)