I ordered 2 of them from Blue Zoo Aquatics a while back.
One of them just dissapeared though. They're supposed to pair up with pistol shrimp and each other, but I never had luck getting them to pair.
LiveAquaria sells pairs of the gobies or trios with the shrimp in the Diver's Den sometimes, but they charge a ridiculous amount for them.
I think I've seen them at Salty Critter before too.