Where do you get a metal coat on platinum?

On Iron Island, with a 5% chance of being held by wild Bronzor, Bronzong, Steelix, Magnemite and Beldum. Well you could do that or after you fight with Riley and beat those two Team Galactic goons you go down that elevator thing and go out the open passage door and go up the stairs and out the door with light coming through and once your outside its right there on the ground. Hope i helped!