Here is where you go to order the letter. S&W does not do the letters, and they don't have the old records any more. The S&W Historical Foundation is now in possession of the records.
Smith & Wesson Historical Foundation - Home Page - Insuring that the rich history of Smith & Wesson will continue for generations to come
Also, just a piece of advice, don't store the gun in the holster. The tannin in the holster can adversely affect the finish on the gun.