Chimecho are found on Mt. Pyre, at the very top where the Red and Blue Orbs are supposed to be. When you scale the mountain, once you get to that area, head to the left or right (I prefer the right), and you'll find a small patch of grass. Inside there, you'll find wild Duskull, Shuppet, and Chimecho.
Be patient, as Chimecho are rare, and it may take some time before you find one.
your either not looking hard enough or your just not looking.
Duskull:This Pokemon is very commong on the inside of Mt.Prye.
Chimecho:This Pokemon can be found in a Half an Hour if you look hard enough.
Chimecho is no the very top of the mountain. The part where the fog is. It's not that hard to find a patch of grass, but it is hard to find a chimecho.