The game's collection data lists Helm of Eldritch Authority as sold by 2 vendor NPCs in Tanaris and Dalaran. The first vendor stands at 51.3, 28.2 on the Tanaris map.
Vendor NPC, zone and position come from the client's collection source tables (CollectableSourceInfo and CollectableSourceVendorSparse); coordinates are the in-game map readout.
Build history
First seen in build 5.5.4.69585 (Mists of Pandaria).
Read from the World of Warcraft client build files (JournalEncounterItem, JournalEncounterCreature, Achievement) and the Blizzard Game Data quest API.
How Helm of Eldritch Authority Compares
Who It Suits
Cloth is the armor type Mage, Priest and Warlock wear. With Intellect, Helm of Eldritch Authority suits Discipline, Holy and Shadow Priest; Arcane, Fire and Frost Mage; Affliction, Demonology and Destruction Warlock.
Transmog Sets
Helm of Eldritch Authority is part of the transmog set Mercurial Regalia (Priest only). The other 16 pieces:
1 other item in the current build is also called Helm of Eldritch Authority. Same-name entries are usually a different rank, faction, quest stage or reward track of the same object.
Blizzard numbers items as they are created, so the named items next to ID 63534 (63528 to 63539) were usually added in the same batch as Helm of Eldritch Authority: the same quest line, zone, vendor or reward set.