I noticed a lot of hits on the post below. I have extensively revised it especially as many links were defunct and I added new information. I hope it helps you on your quest to find and buy the finest papers the planet has to offer before they disappear forever.
One stellar paper-maker not mentioned in my blog is Cave Papers.
Our Smithsonian is a wealth of information for artists:here is a link on all things paper and why handmade is better. Also they used their scientific knowledge to thwart a lie ( John Irving's fake biography of Howard Hughes) and solve a triple murder ( of Mormons of all things).