I found a couple of very nice sites to buy linen and silk:
www.fabrics-store.com - They provide free swatches and the service is great! On my first purchase they sent a 7% off coupon and a swatch card with over 30 different types of linen :)
www.silkbaron.com - Really good site for silks, handmade dupioni, silk velvets, chiffon. They have a great selection on dupioni (all the colors of the rainbow). Andrew Bloom, the owner, works with you personally; very reliable...check it out.