I'm a 55, and in ultimate vault hunter mode and true vault hunter mode I keep going to kill Doc Mercy and he's not once dropped an infinity pistol. I've even done it with 4 people in UVH mode and he just dropped a crummy shield.
any pointers or other places I should be checking for one?
So he said, "Do you love me?" and she said, "No, but that's a real nice ski mask!"
Firstly, farming for the infinity isn't worth it if you're not 61. Only farm for stuff that will help you get through UVHM, like a hornet or hellfire, imo.
Secondly, Doc Mercy's drop rate is glitched. He won't drop the infinity outside of playthrough one.
Was this confirmed at some point? That he WON'T drop it outside of PT 1? I stopped even paying attention to infinities after I got one off of Pete.
I'm too lazy to provide links, but it has been. Some guy/s ran some tests, something about increasing loot chance, and he still dropped nothing, blah blah blah.
Same with McNally, Flynt and the guy who drops the UH.
That would explain why, after I've killed McNally, Flynt, and Mercy dozens of times each, they have dropped almost nothing but money (in Flynt's case, it's literally nothing!). Good to know. I guess I'll go back to leveling one of my other characters...