By "Colt 357" do you mean the model built in the early 1950s on the Officers Model Frame,or the pre-war & much larger New Service? Factory installed layard rings are very rare after 1945,and even many of the later New Services lacked them. This must be a very interesting revolver. Laynard rings can be found on eBay,but tend to run around $25.00. Good luck. Bud