I was able to purchase a European CC card on eBay, redeem it in the U.S., and unlock the pet.
What I've heard is that the opposite won't work--CC cards purchased in the U.S. aren't lockable on computers located outside North America (or maybe the U.S.)
There's a link to an FAQ about this buried in one of the posts that looks fairly up-to-date from what I know of:
ProTip, though: the U.S. Wal-mart Gilded Flutterplume is a pain to find. When I was looking back in June 2013, I had to check four different Wal-marts (in two different states) before I finally tracked one down, and skimming the second post Alrik shared, it looked like it continued to be hit-and-miss months later.