The basic versions of Teir`Dal Adamantite plate drop from the DE group in Kithicor forest https://everquest.allakhazam.com/db/npclist.html?zone=20. From maybe 30+ wipes over the last few weeks I found:
Helm from Adjutant D`kan, Ioltos V`ghera, War Priestess T`zan (x2)
Breastplate from Ioltos V`ghera
Greaves from Brigadier G`tav, Tasi V`ghera, War Priestess T`zan
Vambraces from Brigadier G`tav (x2), Ioltos V`ghera, Tasi V`ghera (x2)
Boots from Adjutant D`kan, Ioltos V`ghera, War Priestess T`zan
Bracers from Adjutant D`kan, Brigadier G`tav (x2)
Gauntlets from Adjutant D`kan, Tasi V`ghera
(so nothing from the robe wearing chanter Coercer Q`ioul or Advisor C`zatl, and probably the General might have these on his loot table too but I only killed him once)
Those two DE's drop the Teir`Dal Chain a little more often (at least it's only been those two of them so far):
Coif from Advisor C`zatl (x3), Coercer Q`ioul (x3)
Tunic from Advisor C`zatl (x3), Coercer Q`ioul (x2)
Leggings from Advisor C`zatl (x3), Coercer Q`ioul (x8)
Sleeves from Advisor C`zatl (x5), Coercer Q`ioul (x1)
Given they all take 8 hours to respawn you're probably better off levelling a DE smith rather than camping them for drops :)