Yeah fuck me. How do you fight disease ? I have 3 serum...
I'm pretty sure I bought a huge stack of serum on one of the Aerodrome leisure flight shops when I was doing the sidequest with the sister airship stewards. I can't remember what route it was, but I have 80 of them and I haven't seen any other shops with serums yet (I just recently got Reddas in my party). I also picked up a some dispel motes on another airship route. I think they sell those fang items too.
On another note, I just wanted to warn others so they can avoid my stress and pain:
keep backup saves on PS+ or USB. The game crashed on me, corrupted a save, and made it so none of my other save files could be recognized to load from. If I hadn't had a cloud save, I'd have had to
beg for someone else's or start a new game.
Last night, the game got stuck on a black screen when zoning from one area to another (into Cerobi from Balfonheim). I exited the game. When I went to load, the game couldn't detect any existing saves. In data management I saw that a save file was corrupted. I could see the other savefiles too, but could not delete the corrupted one.
After downloading a cloud save, the game could again recognize that there were multiple saves. I was finally able to delete the bad file in data management and load from my most recent one. I would have been so mad if I had to go back to my most recent cloud save (before killing hell wyrm). I don't think I could face starting this game over.