The barghest's feed ability (it's [Su]) could give you more HD if you have a way to get [Su] abilities while shapeshifting into outsider forms. Boosting your HD boosts your BAB, unless otherwise noted.

Dusk giants get something similar.

Bards grant temp HD via inspire greatness, which should grant BAB as well. Some people seem to think that the competence bonus to attack rolls is in lieu of the HD-granted BAB, but that's not what it says in the ability. HD grant BAB, unless otherwise noted, and nothing there is noted.