Another one is in the Forbidden Zone dome, in the second floor room, just left of the brain tank.
One can be found on top of the X-13 research facility. In order to reach it, the player character must jump down from the cliff to the north. The cliff can be climbed by jumping up a pile of rocks just to the west of the Big MT west tunnel.
The last one, along with various energy weapon ammunition, is in the same room as above in a chamber connected to the exit platform. It is on a table in the middle of the room, and it is in good condition. This one requires a force field to be disabled in order to gain access to it.
Behind the scenes
The LAER uses the same electric beam weapons technology also developed in the Secret Vault.
The name implies a function like modern attempts at making electrolasers which use lasers to create a conductive plasma conduit in the air and then discharge an electrical differential across the conduit. While practical devices do not yet exist, the concept has been proven and the effect on the target is dependent upon the amount of energy delivered. At lower powers the effect would be much like a stun gun and higher energies being more like a bolt of lightning.