/vp/, what is the best way to get another Metal Coat?

I got a Nincada with Compoundeyes, and I'm aware that Metang can hold one (5% rate) in the wild. How does Compoundeyes work? Do you have to catch the Pokemon with Nincada in the battle or as long as he's in the front of the party? I've caught about 7 Metang at Friend Safari and nothing so far.