Delia's has some pretty nice dresses and so does topshop.
Forever 21 has pretty black dresses, sometimes you can find some at Target too.
Yes, there is indeed a store that stock pretty plus size dresses such as Macy's and JcPenney's. I've shopped there before, but for men's clothing and find that their clothing style is very good.
I go to clique but if you are on a budget I would try a flea market.
the store
You can find many dresses store online.
go to a retail store that sells those dresses and ask them what is needed to do such thing. or offer if you can find employment in another way and find your way to selling the dresses for that store. good luck.
Sassymyprom is the best store to buy your dresses they have different varieties of dresses in their store visit their store for your dresses. buy your dresses from their store
To find cheap dresses you can visit your local thrift store or go to these websites, www.promgirl.com/shop/promdresses-by-price, www.nexteve.com/catalog/casual-dresses/
You might find some pretty dresses at Mango. They specialize in western dresses so Mango is worth giving a try.
You can find big maternity dresses at any department store, like J.C.Penny, Kohls,K-Mart; even you can find them at Walmart. It depends on the name of the store and the price you are willing to pay for it.
Modcloth.com is know for vintage items. Search under dresses, and they may even have a bridesmaids section. You can find affordable dresses there that even the bridesmaids will love.
You will not find Michael Kors dresses at your local big box store but they can be reasonably priced for a special occasion. You are able to find dresses between $49.99 and up depending on the type of dress you are looking for.