These have been floating around for a while, but just in case anyone may have missed them... Pony coloring books are popping up at random Target stories. Of the two reported so far, it sound slike they are always in the dollar bin.
Judging from the cover, they are probably done the same way as the storybook that comes with the 5 pack. In other words, it might be better to just print and color Kloudmutt or Madmax stuff!
But if you are desperate to collect it all, then now you know where to find them!