What material do you need? Does this have to be strong?

Have a look for bicycle flashlight mounts, maybe. They're weak, but one or two might have the required shape.
http://www.dealextreme.com/c/bike-lights-electronics-16075
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10101311 (20GB- backup empeg)
10101466 (2x60GB, Eutronix/GreenLights Blue) (Stolen!)