No wrench? I'd call Griot's and ask for one.
The big thing is that the wrenches for polishers are *very* thin (stamped out of sheet stock) to fit in under the plate. Going off to Sears probably wouldn't work out well as you'd have to grind a normal wrench down a *LOT* to get it to fit.
I bet Griot's would be happy to correct their oversight and send you one.