A note of caution on nickel (or any other metal) plating. Plating adds to the original metal. I doubt that would make much difference to that Ruger, but it can mean that revolver sideplates no longer fit, or that auto pistol slides won't go on the frame until the plating is removed from the rails.
As to a plater, I would just Google "guns nickel plating" and contact some of the names that turn up. Since Ruger does not (AFAIK) make any nickel plated guns, I doubt calling them would help, but they may know of someone.
Jim