I'd check
www.MRarms.com . They offer a line of after market treatments in different colors. The price to coat a entire pistol(all parts) is $155.00. This includes a alloy frame.
FWIW; another gun forum post stated Cabelas treated a few weapons from several major vendors to R&D which brand to suggest to customers who ask. The project ran over a year in places like Alaska & safari trips in Africa.
Reportedly, Bearcoat beat all other services in terms of rust prevention, wear & other factors.