We had some discussion about the availibility of the Fairy Tale Cuvee Champagne outside of the various sitdown restaurants at WDW. You definitely can not it in the outside world, but I speculated that you could probably get it at one of the shops at the hotels.
I can now confirm that my speculation was correct. I saw the Fairy Tale Cuvee for sale at the Poly and the Contemporary. It is in the shop that sales the type of things that you may have forgot to pack, (like toothpaste etc), magazines, etc, among other things.