Phoenix Feather

Hello, this is my first time asking here.

I was wondering about the Phoenix Feather during the Fate/Zero event.
I'm pretty much done with the event, only thing that's left is to farm and completely swipe the shop. I was checking the event guide page, and in the Notable Drops section it says that Phoenix Feathers are obtainable via drops from enemies, or that's what I'm to think since it's with the pages, Black Beast Grease, Homunculi, etc. However I don't seem to recall properly where are they dropped besides First Clears or Quests' drops.
I know they're dropped from Amazoness but I'm not sure if any enemy drops them, so I'd like to know if it's just a mistake or there actually an equivalent to the Amazoness in some farming quests.
Thanks in advance.