Items, NPCs, quests, objects and spells of patch 1.12.1, read live from the realm itself.

Giant Silver Vein

NPC	Level	Zone	Chance
Cliff Breaker Elite	54 - 55	Azshara	80.0%
Cliff Thunderer Elite	53 - 54	Azshara	80.0%
Cliff Walker Elite	52 - 53	Azshara	80.0%