The official release date for the Canterlot Target toys is July 31 according to this post on My Little Pony Arena. They have already been found in Seattle. Check your local Target to see if your store has released them early as well!
In addition, Shine Bright Pinkie Pie will be re-released as part of the Canterlot promotion. She has a slightly altered design.
Have you checked out our G4 Checklist? It's every Friendship of Magic pony and merchandise item we've posted about, with links to the original article. You can access the G4 Checklist (and other useful pages) from the black navigation bar at the top of the page.