ACT labs used to make VGA and S-video versions. They turn up used every once in a while. You may have to wait a year before a pair turn up though.
Stay away from the old ones that use a gameport connection. They work differently than the USB ones.
I have the older raygun style S-video USB model and love them.
They work the way I remember light guns working, not like a wii controller where you have to rely on onscreen crosshairs.