Well quit buying the cheapest tv's you can find

any decent Tube TV will have multiple inputs and outputs. Sony or Toshiba typically will always have them, the no name brands, probably not, those have like one input only.
That being said, then you either need to convert your s-video to composite and plug the gun inline (which kills the quality, since composite versus s-video is a big difference) or you can make a s-video y-cable, keep s-video to the TV, and then on the other end of the Y, convert it to composite for the guns.
The guns DO NOT have to be inline, the just need to see the signal so they can tell what is going on, so be it an output from the TV, or a Y-cable splitting the signal, either way will work.