Real world Vmca, however, is STRONGLY bank dependent.
Not sure I understand this. For certification, bank angle is a variable in the minimisation process that determines Vmca. Vmca will often be limited by the 5 degree maximum bank that can be applied. If more than 5 degrees of bank is applied, the aircraft could fly straight (not necessarily level) at a speed lower than Vmca.
So in what sense is there a dependence? What exactly do you mean by "Vmca" in looking at its bank dependence? I don't think you can even use a "keep it straight" criterion here, because we are discussing turns. What do I run out of? Aileron? Rudder? or something else?