Facebook is pretty much it, there are people with more time than me that scour looking for things like this.
The Majora Game LE was insane to get ahold of though, I feel like it is 90% scalpers right now thought that bought them. I'd like a copy, but I'm not going to pay a premium for it just because Nintendo couldn't be arsed to make enough for demand.
Other stuff though, like Necro said I just sign up for publisher newsletters. NISA and Iffy are quite good about giving a heads up for stuff I want.