Does anyone know any semi-formal dress stores with a size 16?

I am 15, about 220 lbs, and every time that there is a semi-formal dance at our school such as homecoming or winter formal, I always have trouble finding a dress. I've gone to Torrid, but their stuff is all a little bit too busty for me, even in my size, and if I put one on a size smaller, it's too small. Also, Ross doesn't do much for me because there really aren't very many selections for a size 16. Does anyone know where I could find some semi-formal dresses at an affordable price? It would really help me out come school time and I would really appreciate it! :)