They are at MGM. We saw them (twice) in an area that is across form the Commissary. If you are walking towards the back of the park, it's to your left. It is kind of hidden area.
They are inside an area that resembles a loading dock. The Monsters Inc logo is above the door.
They are way back in against the wall. I take it the costumes must be hard to walk in.
The area is very shaded, since it is really inside, with just an open roll up truck sized door. So make sure the settings on your camera can take a decent photo in the shade.