For me Mobley Never drops anything but white items. Gettle has dropped 2 white deaths for me so far and the black queen dropped a derp nukem. But the easiest i have found is either mick zaford or the hodunk guy (whichever you chose to kill) they seem to have a pretty good drop rate. You'll either get a Maggie from Zaford's or a Slagga from Hodunks.
Old slappy is easy. Fast travel to the outwash place and all you have to do is sprint past some stalkers and hot loaders. Then just log out and log back in to use the shops next to the fast travel/spawn point to sell your loot. I've acquired his Orange shotgun and some pretty decent purple gear from him. I'm still on playthrough one with my gunzerker. --- They raided my fridge, stole my wallet, and T-Ped my house. I'm going to London. GT: Red Wolf696
Dukino's mon drops the Mongol, a legendary launcher. Saturn drops the Hive, a unique blue launcher. I'll happily farm for the Hive with you tomorrow cause I've only gotten a lvl 49 one, seems really rare