Repcon test site.. All over the place there....
Their is also one in the coyote den.
One in Primm pass, near the blind deathclaw; one on the top of the hills across the railway just west of there too, just a ways west of the Emergency Service Railyard (tough to find, kinda wedged in some rock clumps up there). Also one laying dead on the west side of the road just a ways south of Ranger Station Charlie, near where the raider gang hangs out (across from the big billboard). Also, they can be found in most of the caves in that area, as well. They are really good at dying. Good thing nobody ever loots them before you come along.