The only company that does NP3 is Robar... however there are similar coatings offered by other companies.
As long as the gun isn't a long gun or has an alloy frame (this company doesn't strip anodizing), I use CCR. Great work, and their prices are very economic (turn around can be slow, but you can save a good amount compared to Robar).
Here are two of mine done in their cera-plate... however, I've done many magazines, bolt assemblies and barrels, as well.
Robar is another great company. I had my home defense 870 and backup J-frame done in NP3 Plus. Nice finish, so I paid the money to have those two guns done. They kept me informed along the way, especially when they had to redo the serial number on the heel (lightened up during the stripping).