www.hostelshoppe.com in their online catalog has mirror section which has a variety of mirrors.
One of these should work ok.
www.nashbar.com search on mirror (mirrors doesn't work!) also has a
few other options. Helmet mounts are my preference though. With the visor clamp on type they have been fairly immune to damage and the field of view is adequate. I use the Third Eye set up, which is very adjustable. Steve