Found today in a Pennsylvania Walmart by community artist PixelKitties, the posters are stocked next to large displays of new pony toys. Much like the San Diego Comic Con poster of last year, these posters are big character collections, and in one case, a newly done map of Equestria. There are four posters available: The Season 2 Cast, Royal Wedding, Villains, and a map of Equestria. The posters are presumably first-come, first-serve till they’re gone.
You can find high-res copies behind the cut.