Do Legendaries only drop once in Borderlands 2?
Savage Lee will spawn every time you load up Three Horns Divide (after you complete and turn in the quest The Road to Sanctuary).
This occurs whether or not he previously dropped an Unkempt Harold, so you can farm him as much as you'd like. This is commonly how players get Harolds with desirable parts such as the double-penetrating prefix and the Torgue grip.