I don't know if you're interested in going the online route, but HTS routinely has those sets in stock there - if you don't mind paying the shipping. I've gotten both the Mos Eisley and Vader's TIE sets there, and haven't seen either of them locally. Actually, I haven't seen any of the new sets at retail, and I don't think our Targets or WMs have any at all right now (or for awhile). TRU here routinely has the X-Wing and Jabba repackaged sets.
I wouldn't be totally sure your areas have even gotten the Dewback wave yet (well, maybe like two cases at Target). I miss out on items, too, but I refuse to believe those sets would have come and gone in my own area without me seeing Arena scenes left behind. Those things are both a prequel item and, well, incredibly lame. I've known when I've missed Vader's Ties because I've seen JSFs here and there - and it's a way better offering.
I'm not sure I've heard anybody east of California mention a find at Wal-mart. Target and TRU sightings, sure, but a ton of Wal-marts don't seem to have carried anything except the Jabba/Biggs wave (i.e. don't seem to have ordered anything since 7/26).