I am a bit larger than the largest size at LB, Catherine's, Avenue, etc. I love Zaftique for cute plus-size tops (haven't tried the pants yet). They're a little pricy, but the quality is good.
Also, I recently found a website selling Indian-style clothing called eShakti. They offer standard sizing, and if you send them your measurements, they'll custom-make the clothing for you. I contacted them to see if there was an upcharge for custom items, and they said there is not. I haven't ordered anything yet, but probably will in the near future.