When I ducked into Wal-Mart to do my daily wedding ponies & posters check, I noticed a new display of those 'Giant' $1 colouring books just inside the door! It had to have just gone up, because we were there yesterday and didn't see it (it didn't look like anyone else had even purchased from it yet). And guess what?
LUNA'S ON THE COVER!
Actually, it's Celestia on one side, and Luna and Celestia on the other. The colouring pages and activities seem to be more-or-less the same as the previous book (with the Mane Six and Spike on the cover) - there are one or two differences that are so minor as to not be worth mentioning, but it DOES have the Luna page! So if you missed out on getting that the last time around or you just want a book with Luna on the cover (I sure did!), you may get another chance!
If you haven't seen them at all yet - they're very tall, thin books with around 24 pages, with each page having either a large picture of a cast member to colour or a very simple activity. They're usually in a cardboard display box with various other character colouring books (like Hello Kitty) - this one was the first thing I saw after walking in today, but I've also seen the displays in the back, near Electronics, or with the rest of the books.
(Edited to add location - this was at a Wal-Mart in smallish town southeast Georgia!)