Have you been to Forth & Towne? I know they have a store in Chicago -- it's the new store in the Gap/Banana/Old Navy empire, and the clothes are probably at the Banana price point and style, but they have a larger range of sizes (up to 20 in the store). They have some really really cute dresses right now, so you should check them out (but quickly, because the stores are all closing by the end of June).