Snap a few good pics with your phone and head to the local bike shop. they more than likely have asome spares or a box of used parts you can glean one from.
It is not uncommon for these to be missing on "New to me" bikes. If your LBS doesn't have one Niagara has just the nut and bolt or the whole claw.
Nut/bolt
http://www.niagaracycle.com/product_...ducts_id=10676
Claw
http://www.niagaracycle.com/product_...oducts_id=5148
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk