I've been able to narrow it down to where you can find 2 at a time.
In Henderson, in the dead zone named Metzger Sloat's Hideout. It's quite close, about 50 meters South, South East from the center of the Old Town Cinema.
One can be found diagonally to the right on a shelf once you go through the double doors that lead you to the undead. The other one I believe is in the middle cage to the left that holds all the computer equipment you can open. It's not on the same shelf as the computers but just opposite it. (Could be wrong about the location of this one, but it's defiantly in the room somewhere)