GunCon3 uses infrared LED emitters which are positioned on top of the TV. Because the gun triangulated position based on sensors, it can be used with any kind of display, from CRT, to flat panel, to projector. GunCon3 guns are quite rare and expensive, but hopefully aftermarket emitters give life to guns that have long since been separated from their originals.
To install, simply remove the adhesive backing, and stick to the back of the TV along the top edge so the IR LEDs are visible. Plug the USB-A end of one cable into the tv and the other end into one emitter. Next, take the second cable and connect the two emitters. The emitters will glow red when properly working. Combined, the emitters draws 270mA at 5V.