I'm having the same problem with my newly purchased Yamato "Perfect Trance VF-1J Ichijyou Hikaru Type with Super Parts 1/60." I bought it through newegg.com but the merchant was Treasure Island Sports (http://tisinc99.com). Anyway, the darn thing broke on the very first transform. I was watching the transform instructions while doing it, so I tried to be careful with the shoulder, but to no avail. Dang thing cracked.
Anyway, I tried tisinc99 but they haven't returned my emails. I tried hlj.com but they said I didn't buy it from them, so...no love. Yamato won't sell them to round-eyes (OK well Americans because of the whole licensing thing). So I'm at a bit of a loss.
Fortunately I bought a couple Bandai 1/55s for my kids. I had Jetfire when I was a kid so that's how I go into all this. I never watched Robotech until the last month or so. Actually Robotech kind-of sucks, really. Love the toys though. The Yamato is gorgeous but is a fragile POS. They should have used a lot more die cast in the shoulders. The Bandais are much more solidly built. Different types of toys really.
Anyway, if anyone has any leads on replacement hinges, I need two for sure. Otherwise I'll just be stealing my kids stuff...