There are 4 unique codex entries in the Bestiary section on Imperial Balmorra. 3 are accessible to all players regardless of class or faction and 1 is faction specific.
Bormu is obtained near a proximity map trigger.
Codex type: Bestiary | Faction: Both | Class: All
Associated Achievement: Imperial Beastmaster of Balmorra
Mutated Colicoid is obtained from killing a Mutated Colicoid Drone. The Mutated Colcoid Drones that spawn in front of Hazard Vault 305 have a long respawn time. You can jump partway up the cliffs on the western side of the map and summon your companion and then order them to target the drones on the plateau to unlock this achievement.
Codex type: Bestiary | Faction: Imperial | Class: All
Associated Achievement: Imperial Beastmaster of Balmorra
Wingmaw is obtained from killing a Ravenous Darkpyre.
Codex type: Bestiary | Faction: Both | Class: All
Associated Achievement: Imperial Beastmaster of Balmorra
Zeldrate is obtained from killing a Tainted Zeldrate Mother.
Coordinates: -1016, 162 | -1041, 334 | -942, 450
Codex type: Bestiary | Faction: Both | Class: All
Associated Achievement: Imperial Beastmaster of Balmorra