I haven't seen these yet around here, but I've been looking. Both Target and TRU have been sold out of these for awhile, and haven't restocked, and Wal-Mart has a few of the Han/Greedo wave sets on the pegs. I think the newer ones "may" have been there recently, but I don't know what they are all packed with. I saw the Bespin/Hoth sets, as well as some repacked figures on the red/black cards.
I agree, I really enjoy picking these up too - nice and simple. They do seem to sell quickly though, at least around here. In the past I've often preordered them through BBTS, but that's getting more expensive. I've got the next couple waves preordered just in case, but the prices are closer to $8 per two pack now, and that starts getting a little steep. Hasbro seems to have a good thing going with this concept now though, as the Marvel packs seem to be selling pretty good here too.