Used electronic gear shops. You might very well have trouble finding a decently setup deck for live recording which is also a double. (If you want a dual to bang off practice tapes for everybody, that might be a problem too--my experience is that the dual drives get a bit wonky and don't run at exactly matching speeds after awhile, so the dubs are not in tune with the masters.)

Frankly if you still want to use cassette, I would be getting a 4-track--should be able to find one for a couple of hundred or less now.