source for Mafac brake lever clamp?

Through my own carelessness, I've somehow lost one of the brake lever
clamps on my perfect old Mafac Competition levers, which I need for the
moustache bars on my old tourer. The levers are just like these he
http://www.mindspring.com/~d.g1/randon.htm. Does anyone know where I
can find a replacement clamp? Incredibly, I still have the hex nut which
threads onto the bolt which tightens the clamp -- but no clamp!

Thanks very much!

Art Strum
Mountain View, CA