Okay, when we were in DL in December, I was on the hunt for a 3XL shirt for myself. It was a long and lean hunt!!
In the end, there were no shirts at World of Disney in DTD. I did find three styles of the same shirt in up to 4XL, I think, at the first store on the left as you walk down Main Street, just past the firehall. They were at the back and I had to ask the CM to help me find some.
Actually, I'm wearing it now. Cute Tink shirt. Seems to me there was a Mickey one, and one other.
Good luck with the hunt.
Let us know if you find any. I think that Disney is making a big mistake and losing out on lots of money by not tapping into the plus size market.