If you've been inspired to look for stereo equipment at your local thrift store, I need to add one more caveat. The paper and foam in stereo speakers deteriorates over time. If possible, pull the grill of any prospective speaker purchase from a thrift store. You might find that the speaker looks like this --
-- or like this:
Unless you just want to by vintage stereo speakers as a restoration project, I wouldn't recommend buying speakers unless you can confirm that they are in good shape and working. Otherwise, you can buy perfectly good speakers online or at your local stereo store.