In the Plane of Fear: Rogue
In Fear Itself: Summons.
In Feerrott, the Dream: Part of the "Ritual of Terror" raid event (see this quest entry for event information and loot).
In Zeixshi-Kar's Awakening: These are immune to root/snare.
In Crystal Caverns, Fragment of Fear: Hits for a max ~12,000; does not see invis.
In Heart of Fear: The Threshold: Hits for a max ~13,800; does not see invis.