Naturally, you're right that TGC don't distribute FPSC games. They've been known to redistribute Firewall, a DBP game (an excellent one at that), but remember that that's a top notch game--mention the word "stock" in FPSC and you're guarenteed a no. All custom stuff is still almost entirely unlikely, but I suppose you never know.
They also used to resell Trackmania: Sunrise (excellent game, by the way), but that's a professional game made in C, so...
Basically, if you're going to sell an FPSC game, you'll need to do it yourself as AE outlined. You'll also need to make sure it's incredibly good.
Evil has a new name. Demo out now!