Okay, they're not technically Madballs, they're "Mutant Monsters"... which are just knockoffs of Madballs. The green one is Slobulus (from Amtoy in the '80s) and the blue one is Repvile (from Art Asylum in the '00s), and the red one is apparently an original design: although Kidrobot has done a Madball with a facehugger on it, this is a three-eyed alien with an exposed brain, not a human with a ballcap.
The balls can be found in the "impulse buy" bins right at the front of the store. If you're at all interested, get 'em quick, because we can't see these getting restocked.
damn, I went today and that part was already full of Christmas stuff. No Madballs for me, I guess...