I've been seeing a lot of posts lately about people getting legendaries like candy on Halloween. I think one guy said he found some from junk loaders in arid nexus. Should I go there? I wanna get in on this action lol --- I have Dysarthria. It's a Speech problem. Your question is answered now.
They drop mostly from bosses and names enemies. They can also drop from random chests and the like. There's a list of them all and where they drop off on a message board here. It's a low chance to drop, so you have to farm them.
Just play the game. The general condenses is that today drop rates on rare gear have increased across the board. No one has testes mercy yet, but people are getting things from enemies that they wouldn't normally drop. I. E. Junk loaders dropping kerblaster & bouncing bonnie.
Your best bet is probably the warrior & tera for the amount of loot they drop. Other than that go somewhere where a lot of SBadass enemies spawn. --- Oh, you thought they made this game for you? You clearly bought the wrong game.