I ordered mine online. They are fantastic - cheap, durable, clip into eggcrate easily and versatile for mounting frags several different ways. I have tried others and would never go back. I got them from Uberfrags and I believe they are called "Coral cradles."
http://www.coralcradle.com/
you can also get them from Premium aquatics and Custom Aquatics for around $0.35 each.
Mat