Not sure if you've stopped looking at your original post, but I wanted to give some advice on dress shopping. First and foremost, please don't go to David's in Dedham. I had two horrendous experiences there. The David's in Natick has been my home-base and the ladies there are great. Just recently I went back to Natick, freaking out about if I needed straps on my dress....the very nice ladies (of all shapes and sizes) calmed me down, showed me some options and I just really can't say enough about them.
I went to VOWS - they do carry some dresses in larger sizes. I'm a street size 18 and I was able to fit into some dresses. They definitely don't have a ton.
I would also recommend Chryssie's in Canton, MA. I was really impressed with the wonderful, wonderful, wonderful women who work there. They have quite a bit of size selection and always made me feel beautiful in their dresses. If I hadn't already fallen for a dress at David's, I would have bought my dress here.
Good luck! It's so difficult when the dresses don't actually fit. I think you also got a ton of great suggestions for places I was going to suggest from other brides.
Hugs!