I found large sheets of foamcore at Wal-mart for under $5, I sliced some 2″ strips, out of which I cut rectangles of varying sizes. All/No doesn’t need a big rectangle, but P/non-P does.
I also found magnet strips in the craft section. They are backed with tape, and can be cut to make the teacher pieces.
Okay. I’ll show you how I do the Contrapositive.
Slapping these cards on the metallic whiteboard is very satisfying.