Quick update for those hunting. Thanks to some tips from fellow spies, have some more info.
Looks like so far there are 8 boxes: 4 character boxes each with two backs representing left/right halves of character faces.
1 4-pack of cups, featuring Vader and Yoda
2 Single cups, featuring Vader or R2
I purchased and entire case (12 boxes) of mac and only got three different boxes (4 each), so this will require more hunting to track them all down. Target carries the boxes, and larger Target stores may carry the 4-packs of cups.