They are unique, so I assume they randomly drop like all other uniques seemingly do. Maybe certain end game maps will increase drop chance.
Some masters sell unique items for Choas Orbs once you get them high enough, like level 8 or so.
I think I might start with the witch. Just to try something different. Although it does look difficult to optimize the class.
Today just sucks... it's NEVER going to be 10pm!!