I've seen photos of the exterior of his store in Nairobi on the web but can't seem to find them now. The name also appears in the Kenya Gazette from the 1920's in published notices about stored firearms, etc. I've seen a number of Mauser Type A's with Heyer markings on the barrel and have one of them myself. (There's a Type A in 9.3 x 62 with Heyer markings in the current Poulins auction but it has a non original vent pad). Apparently he was the largest safari outfitter in East Africa during the late Colonial years, and possibly before. I've seen the Heyer markings on at least one gun other than a Mauser - possibly a Mannlicher or Zi-Di.

I'd love to see photos of the interior of the store if any exist.