Try local consignment stores. They're desperate for plus sized clothing, especially good quality pieces. The one I used was in a nice area of town, so had a clientele that could afford pricier clothing. I made a nice little bundle to add to my Whole New Wardrobe fund.

As a matter of fact, they kept calling me for a year or two, hoping that I had more larger sized clothing. Apparently the plus sizes go like hotcakes.
Good luck!