I've been collecting these things for years and the true original used by Clint Eastwood in the movie was made by Bucheimer-Clark. (I had one at the time for my 6" Md. 27.) Bucheimer was an east coast holster mfr. who purchased Clark, an LA area holster mfr., and then combined their product line. Cattle Baron and Lawman Leather came into play after Bucheimer/Clark went out of business.
They did in fact make these same holsters for 4" K-frame guns and sold them to the military because I have one made during the Vietnam War, complete with the Gov't inventory number stamped inside the leather.
I also have some older Clark shoulder holsters (1940's era) and it is easy to trace the development of this holster once you start with the Clark holsters and work your way forward.
As for someone making a copy of the holster, the big problem is the shape of the flat, somewhat C-shaped, retention spring that encompasses the revolver's cylinder and is sewn inside the holster. It is the secret to the whole design and without it, the holster is more or less just another under the armpit holster.
All The Best,
Frank W. James