This is a map that shows the locations of most herb nodes in Tenebra. You need to have the Herbalism profession in order to see and gather herbs. Some of these nodes require skill level 190, while others need 240. You can train up to level 190+ in lower level areas, and then increase your skill by gathering the level 190 nodes in Tenebra.
You can submit additional spots by uploading a screenshot and linking it here.