Actually, I have the first part of Prometheum Exxet translated, and have been meaning to post it, including the very brief write up they give of Alchemy and the other couple of skills for enchanting purposes. I'll try and get that up tomorrow sometime. The artifacts I haven't even touched yet, and really am debating on that.
That being said, as far as I know, there is no list of herbs by the different regions, so it's up to you on that one. I don't recall any specifically mentioned in Gaia, Vol. 1, but I could be forgetting something.
Also, though Alchemy is written up in PE, it isn't really given a lot of meat, so to speak, as it is used primarily as an enchanting skill. So, I know I will be using it in my game to add some additional stuff. I loved the Alchemical items idea from D&D 3.X, so will be including those, and how they work in my newest Anima game that just started up. Also, Elric of Melnibone posted an Alchemy system based on Full Metal Alchemist here: http://www.fantasyflightgames.com/edge_foros_discusion.asp?efid=85&efcid=3&efidt=570934&efpag=1#575850
It could be worth your while to check it out and see if it might help a little bit. Just an idea.
Edit: Actually, here's the Google Docs Link to Chapter 2 of Promethium Exxet. Alchemy is listed at the end.https://docs.google.com/open?id=0B0GlXCzYFgcUNGQ2M2ZkZTctMTlkMC00MjRhLWE2ODItZDA4ZjNiY2E4MGNl