In Terokkar Forest there is a subzone at 22.10~ called The Barrier Hills which is only reachable with flying mount.
Everytime I go there I find 3-4 Mana Thistle and spot a few Adamantite.
The respawn isnt very long so if you got nothing to do as Miner or Herbalist go there and check once in a while.
EDIT: While writing this thread 2 of them had already respawned