Garnets (of any color/variety) and tourmaline (of any color).
Sorry @westofhere and PSers, I apologize for my post. @westofhere was asking for vendors, not private sellers.
I love cabs and I don't think I recall many (any?) garnets or tourmalines.
Mostly opaque semi-precious, plus of course sapphire, any star corundum, and chrysoberyl. And occasional emeralds in antiques.