Finding a Zenith TU4C for D4 7U

I am pretty sure my pony carb is toast. Too many years exposed to water and just plain old age. I have looked around and can only seem to find rebuild kits. I would prefer to just find a already rebuilt one and eat the core charge. Where can I get one? Believe it is a TU4C Zenith 1951 D4 7U 12xxx serial number range. Also seem to have a magneto that is only firing part of the time preventing it from starting. This machine is basically sold but I have to have it running.