I am afraid it is a wanted requirement.
I don't know if it requires a min rank or just to have the skill as class skill. You may need only 1 level (or few levels) of either Ranger or Druid to qualify, and the rest can be Barbarian (you would call yourself a Barbarian if you were Brb10/Dru1, after all).
IIRC, in S&S there is one feat that lets high level Bards use ANY skill untrained, including exclusive skills (but maybe not psionic skills?), which may qualify a single-class Bard.