I bought one at my local parts store, Lisle brand IIRC.

It's similar to this one.
http://www.ebay.com/itm/2705-ALTERNATOR-BELT-TIGHTENER-HOOK-/200922697065?hash=item2ec7ed0d69:g:9ooAAOSwVFlT3dAl&item=200922697065&vxp=mtr