I recently found a 1940 Colt Shooting Master 357 with a King Cockeyed hammer, rear sight and (apparently) action job. A fellow forum member was king enough to point me to an eBay auction for a 1939 King Gun Sight Company Catalog reproduced by Cornell Publications. They were located in San Francisco if you can believe that!
Here’s a pic of the rear sight:
Although mine is a Colt, I think King fitted the same rear sight to Smith & Wessons. Also you can see the quality of the fitment King did. Bottom line - I don’t think the rear sight on the OP’s revolver came from King although the hammer certainly did.