On another thread earlier today, someone reported calling the BBB and them saying they currently didn't have any frozen dresses and weren't expecting any until April or May, or even later...
Now, take that last bit with a grain of salt, I'm not sure that the CM's working there always know what the supply chain looks like, so it's possible more could come in at anytime.
However - if you are looking for a frozen dress, I would suggest getting one ahead of time at
disneystore.com. They currently have Anna's blue dress, and there are reports that they are getting in a version of the green coronation dress (someone nabbed one at an actual
disney store in NYC). The Elsa dress is the holy grail right now, but I would keep checking the disneystore.com website daily - a few weeks ago they had some in for about 48 hours, and then they were sold out again.
JC Penny also has sort of a "mini" disney store inside it. I was at one today. They had Anna's blue dress, but not any Elsa merchandise. Some people have had good luck with Penny's, since not everyone thinks to look there, and the Elsa dresses were supposed to be nice. The Anna one I saw today was a pretty nice one. I like the disneystore one better, but that's just IMO. The Penny's one was also only $36, compared to $50 for the disneystore one.