I checked the 6 keyboards at my house and none fit. The Dell Quietkey came closest, but it would take some Dremel work.
If it were me, I would cut a template out of a piece of paper or cardboard and put it in my wallet. Whenever you go back to the thrift store, check whatever junk keyboards they have against it. You may get lucky, and the $2 for the keyboard would be what you would have paid for shipping anyway. Then give the keyboard back and let them sell it again!
In the meantime, use the binder clip.