You see, I want to get a shiny using the Masuda method, but they say the ditto needs to be foreign but could it be the Pokemon you want to be a shiny, in my case, Metang?
Yes. The Masuda method works by breeding 2 Pokemon from 2 different regions, not just a foreign Ditto, so it will work.
Source: http://bulbapedia.bulbagarden.net/wiki/Masuda_method