Hellfire Boltcaster
This is a boltcaster that makes enemies burst into flames instead of being knocked out. Its inside the Nassif greenhouse and is slightly difficult to get. Go through the warehouse and into the office, then make a left in the hall (away from hydroponics control). Then, save the game when you get to the balcony save (so you do not have to run all the way around). Carefully jump to the beams sticking out on the other side of the rail. Then, jump to the ledge to your right. It is small, but you can stand on it. Use the outcropping window as a foothold to jump up onto the balcony above you, then go through the vent shaft. In this room you will find the weapon in the corner amidst some junk.
There is a hidden Boltcaster in the Tarsus Academy in Seattle. Go to your room and Billie will tell you to look up at the ceiling. It will disappear. Then, jump and climb up onto the ledge above the counter. Jump to the other side and you will find a Boltcaster.