I finished all the quests but...

You have to do all of Lita Lawless's Bounty Hunter quests: Fool's Gold (40), Rags to Riches (Level 70), One Step A Head (Level 75) and Catch A Bigfoot by the Toe(Level 80). The return to Lita Lawless after completing the four aforementioned quests and talk to her about "Bounty Master" (Level 80), then talk to her again and you'll receive your reward.

Edit: Turns out StrategyWiki already has this quest! Right here... For future reference: If you ever have quest related advice search for it on StrategyWiki, as Isaac and whoever else contributes will most likely have added it by the time you ask...