Silver nitride....no. But there are a lot of outfits doing hard chrome and nickel plating of guns. The only exposure I've had to those types of finishes is through the trap shooting community. A couple of the more popular options are Doug Braker at
http://dougsgunsmithshop.com/index.cfm/pageid/15 and Dan Lokker at
http://www.giacomosportingusa.com/Neither does the plating in-house. They have the gun expertise and deal with others who have the plating expertise. For a one-off project, I'd prefer to deal with one of them rather than directly with the metal finishers.
