I've been taking apart some common electronics looking for a TIP31C (TO-220) transistor, but all I'm finding are TO-92's. Anybody know where I can look to at least find one from the TIP series?
That's a power transistor, so you would need to find something that actually handles a decent amount of power -- audio amplifiers, power supplies, motor controllers...
Or, you can buy it from an electronic component store. Those are one of the most common power BJT's so any electronics store should have it. If you're not afraid of buying online you can get them from many sites...