I tried to craft the Philosopher's stone, the recipe includes Purple Lotus. I headed to Azshara, where according to wotlkdtb.com, it spawns, I didn't manage to find any. The auction price is insanely high, so what is the matter with it?
There is one 2016 post about the absence of this herb, but it doesn't really clarify anything for me.
I think The Hinterlands is where I've found most of mine in the past. I know I've seen it somewhere else too, but I don't remember where. I remember fighting a plagued bear near it though, so it was probably Western Plaguelands or Felwood.