Dwarven Sage Robes from the Southern Shiverpeaks ex-salvages out to bolts of silk too; and I think a couple of some kind of robes (sorry, I'm old and my memory for things like this isn't what it used to be) in the desert did too. I'm up to 17 bolts of silk :-)
silk is the least exspensive rare material in the game. but characters earlier in the game might not be able to make 100 gold so easily, so try going to the crafter outside of sardelac sanitarium. he might craft silk.
