"a goblin caster" should be spawning at the double igloo goblin camp in the southwest tundra of Everfrost Peaks. The coordinates are about -990, -1575.
The casters drop Shattered Caster Beads or Caster Beads to be turned into Shamus Felligan in Halas outside the shaman guild. The Gavel of Justice is given as a reward for turning in the Caster Beads.
Currently only goblin scouts, divers, and whelps are spawning in that camp.
http://everquest.allakhazam.com/db/quest.html?quest=227