I think your talking about Storm bows. They drop in Underworld pretty often. You have to have The Temple of Ages on your map and I'd recommend getting through most of the game before you go in the Underworld.
stirnviws are tight especially if you find that one ultimate bow. and they dont drop often ive only gotten 2 stormbows, 3 eternel shields, and weapons, i think arena shoul add more drops to this underworld. for 1k i dont go there anymore im focused on pvp now.