There are 4 bestiary entries on the Imperial faction version of Balmorra. All four are required for the Imperial Beastmaster of Balmorra achievement.
The Borum codex entry proximity location.
Codex type: Bestiary
Codex location: Balmorra: Markaran Plains
Codex coordinates: -1288, 1304
Faction: Empire
Class: Bounty Hunter - Imperial Agent - Sith Inquisitor - Sith Warrior
Associated Achievement: Imperial Beastmaster of Balmorra
A Mutated Colicoid codex entry location obtained from a Mutated Colicoid Drone.
Codex type: Bestiary
Codex location: Balmorra: Sundari Flatlands: Balmorran Arms Factory: Power Center
Codex coordinates: 1195, 219
Faction: Empire
Class: Bounty Hunter - Imperial Agent - Sith Inquisitor - Sith Warrior
Associated Achievement Imperial Beastmaster of Balmorra
A Wingmaw codex entry location obtained from a Revenous Darkpyre.
Codex type: Bestiary
Codex location: Balmorra: Sundari Flatlands
Codex coordinates: 1035, 1404
Faction: Empire
Class: Bounty Hunter - Imperial Agent - Sith Inquisitor - Sith Warrior
Associated Achievement Imperial Beastmaster of Balmorra
The Zeldrate codex entry location obtained from the Tainted Zeldrate Mother.
Codex type: Bestiary
Codex location: Balmorra: Markaran Plains
Codex coordinates: -1038, 332
Faction: Empire
Class: Bounty Hunter - Imperial Agent - Sith Inquisitor - Sith Warrior
Associated Achievement Imperial Beastmaster of Balmorra