Just got a new Lee catalog in the mail today. They list a mold the size of the six cavity that has 18 cavities for OO buckshot. 3 buckshot are cast hooked together by a strand of lead. So basically a six cavity as there are six holes in the sprue plate.
I know many here that like casting shot so this will probably be a way to cast them.
The list price in the catalog is $62 compared to $52 for a standard 6 cavity. I imagine sale price will be around $40 to $50.