If you go back into Pyro Petes Bar before completing the mission "A Montage", if you save and exit you will spawn inside the bar. Take the first right and an elevator will take you to where you fought the previous boss.
The boss will not spawn but the loot stall to the left of the elevator and two red chests in the jail room do.
So far I havent gotten anything great but it takes less than 30 seconds to loot all three chests. Hoping for a legendary soldier mod in one of them haha!
Someone else should try this out and see if it works for them. I've gotten 2 e-techs and 2 purples so far and quite a few blues. I'm not saying its better than the pirates one but some people have this that don't have the pirates dlc.