Supposedly Tier 1 Swamp Fiber could be found in the Antiquarian Swamp realm, but all I can harvest is Tier 2. Also, I heard there was some at the Essence trader, but there was none. Perhaps I bought it all before or maybe my other party members did, but it's required to make slight curative potions required for a quest.
I finally found it in the Provisioner reslm. But I thought Antiquarioan < Provisioner so this seems like a bug