Complete the Lovely Charm Bracelet daily quest for each Horde capital.
This achievement will take:
Back in Wrath, players could take a demolisher in Ulduar and kill the iron dwarves to earn a ton of the charms. (It was patched as soon as possible by Blizzard for obvious reasons.) Since Cataclysm, players have been using the continuously-spawning (as long as you didn't kill the sentries at the end of the hall) Unstable Corruptions in Throne of Tides. Unfortunately, it appears Blizzard finally put the kibosh on this with a hotfix this year. ("Lovely Charms should no longer be incorrectly awarded from Unstable Corruptions or Mutant Parasites." Source)
Lovely Charms can be collected from any "worthwhile enemy" (i.e.: a killing blow on an enemy that yields experience or honor), so don't be discouraged. The bracelets themselves are not soulbound, so they can be traded to other people. You can try soliciting offers in Trade channel if you really do not want to kill things for yourself.