I think I have only seen the "Big Three" in one store besides Target. Target is probably the best place to find all five. They also exclusively have the retro packaging at Target. For whatever reason, they have not been stocked in the cereal aisle. I have seen them either at the end caps at the registers or in the Halloween section.
I had never heard of Brute or Mummy before this year either. I remember seeing the other three on the shelves. Boo Berry did seem to be pretty scarce most of the time.