Cerberus Limb has restrictions on where or how it can drop. It cannot be chanced.
Cerberus Limb drops from Ahuatotli, the Blind, the most common boss among the 3 bosses of the Azurite Mine. His node, The Grand Architect's Temple, can potentially spawn in the Vaal Outpost biome.
Monster restrictions
This item can be acquired from the following monsters: