Is there a cheap supergun that can output ntsc? I tired to find one but superguns of any variety are hard to find
There isn't really any such product as a "supergun", and I'm not even sure where it got that stupid name. It's the sort of thing you build yourself. The rest of us call it a "Jamma test rig"

There's nothing really to it, it's just a Jamma harness, power supply and controller/video connectors. The thing is that Jamma arcade boards output RGB video to be used with an arcade monitor. If you want to use the board with something other than an arcade monitor, you have to convert the RGB video from the game board to composite or s-video.
Another option is to simply use a monitor that accepts RGB video directly. This will always give you the best picture. Arcade monitors are not the only thing that can accept 15.75khz RGB video - a lot of older computer monitors (pre-PC) used it as well. European TV sets frequently have RGB inputs as well. Here is a picture of my test rig ("supergun"):
I use it for repairing and testing arcade boards. I use Sega Genesis controllers because they take up a lot less space than an arcade panel. The monitor is an Apple IIgs RGB monitor.
Inside the box is a modified PC power supply, a speaker, an isolation transformer (for powering arcade monitors), and that's about it. The front panel buttons are the Jamma Test/Service/Slam switches, and Player1/Player2 start and credit.
-Ian