The Alice dress is hard to find. I would search Ebay. It seems to not be in all the stores at WDW. Also, if you are getting the park version, that dress runs VERY small. The head hole doesn't stretch and it was a struggle to get my DD's head through and she is just average sized. I would go with a 10 or even bigger if you can find one. Also if you get it a bit bigger they last a bit longer to. My DD seemes to be growing about a foot a year (OK, slight exageration) and dresses that I bought to just fit for the trip are packed away or sold now because she coudn't wear them much longer for anything else. We bought a generic Rapunzel dress last year. The site siad it ran big, but it DIDN'T! I would've gotten her an 8, but instead got her a 6. She is wearing it for Halooween, but it is a bit too small, especially in length. But for the money we spent, she is getting one last use out of it!
Here is a picture of it. This angle doesn't look too bad, but it is about 2 inches too short and her waist sits a bit higher than it should. Also very snug in the mid section.