Yeah, all the B3 maps are random chance. There are 2 maps where you can get the 'Hero.' There's the Hero Base, which is a random spawn, and there is the 'Every Girl Lineup' room that also grants a star. You'll want several aphrodesiac potions for that one, as the last column of bosses can be quite taxing. If you don't have enough capture stones, save them for the higher level girls.
To get 'extra' chances at them, save your clock-/step- items. Once you complete a b3, use 4 step- items to set the step down 4 before leaving the B3 room. This lets you do another round of Regular/B1/B2/B3 for more super items.
I realized I missed a portion of the game when looking at the Achievements room. There are several achievements for going far into a run without upgrading, or for beating each boss without increasing STR. Those make for some fairly exciting and challenging runs, especially once the game gets easy when you've purchased all the in-base upgrades.
