I got one from Bachman a few years ago, and did some conversions on it. They are really fun guns, very accurate and after the conversion, very ergonomic...like the UMP. The barrel comes out just like the UMP (easily) and can be cut and profiled like a UMP. With the ban gone, you can get the UMP mags and conversion lower is fairly easy.
The converted ones at shows usually bring a premium, it's best to buy the stock USC, then get the conversion parts, and finally dye the ugly grey color to black (very simple and cheap to do).
There are several stock and modified USCs on Gunsamerica, you could prob start there and work your way to a dealer here in the DFW area. Spreadfire arms always has some UMPs at the shows, so you might call him and see...that is if he ever even deals in USCs since he's pretty straight up Class 3 toys.