The promotion is going to run from June 18-July 13. I would assume it's pretty much anywhere that sells Frito Lay Chips.
It's most likely a send-in program (collect so many UPCs plus shipping & handling). Cause you can imagine the sheer Kaos (pun intended) that a figure inside a bag would cause. There would be people just ripping open the bags and taking the figures. This happens often with certain magazines when they gave away CCG cards.
Apparently there is also a rumor that on June 27th the new figures for Giants might start hitting the stores. Or perhaps one last wave of regular Skylanders?