Japanese clothing tend to be for small size. Here are some sites that offer larger sizes. Beware medium usually means large and most clothes aren't meant for wear very large sizes. My blog does not condone obesity.
From China they have plus sizes and they tell from which season that item is from. Plus the prices are really cheap and most of the items are made of cotton. I like that you get to select your shipping method so you might get cheap shipping.
Also from China. They offer more and also signifigantly cheap.
China. shipping is expensive.
assuming from china . They only offer dresses for larger sizes and their shipping is super expensive.
From singapore. They cost a bit more then chinese sellers but their shipping price appears to be very low