Royalwood is the best linen supplier. For C-Lon cord, I always go to
http://www.store.jewelsinfiber.com/. Marion always ships super fast and has a great tool and supply section. Plus findings for Kumihimo braids, which I love making.
For hemp, I've tried several different suppliers. But lately I've ordered it all from KwikCrafts,
http://kwikcrafts.com/crafts/category/Hemp.html. They have a great color and variety of different hemp thicknesses. Plus they have Hemptique hemp, which is pricier, but totally worth it. So soft and uniform, and resists separating into individual fibers.