I've been playing TDS since mid-December. Most of the original bitizens are unlocked, but several originals are not--R2D2 for example. I'm not sure what in-game actions will naturally unlock them. I don't want to spend bux on it. Any insights out there re: this game rule?
There is no specific way to unlock them. They seem to be date based or based on the number of levels. With a recent Monday update that added new levels everyone received Togruta, Bespin Han, and several others.
So if you don't want to spend Bux, just keep playing and be patient. They'll unlock eventually.