I used these people for quite a long time now for firearms plating of engraved guns.
Custom Gold & Silver Plating, Antique Finishing: Reliable Electroplating: Chartley, MA
They also do plating stripping,,listed under 'secondary services''.
They do not do any gunsmith work, so the parts will have to be sent 'disassembled'.
They do have an FFL to cover firearms work.
They were always fast..turnaround on plating jobs was within 2 weeks.
FWIW,,I seem to recall when I had guns plated in silver, they told me one time that they undercoated with copper, then nickel, then the silver.
No matter.
Quite a few engravers and custom gunsmiths use them for plating. They've been around for a long time.
Since you only need the plating strip services,,most any Electroplating shop can do that.
The problem is when you mention those bad words,,Firearm or Gun Parts..
Many will then just say no to the work or they may not have an 01 or 07 FFL to cover themselves.
The proper polishing of the parts after the plating has been removed is the real art. That will decide wether the guns return to their original looks or just become a blued version of a refinished nickel plated gun.