Obtaining Poultron and earning the achievement requires you to corral 5 cyborg chickens around Colorado Springs into the chicken coop at your Ranger HQ, luckily one of the 5 is already in there and thus you need to find the other four. Doing this requires you to find the Cyborg Chickens as well as have the appropriate Animal Whisperer rank (5) to convince them to follow you so you can lead them back to the chicken coop.

The first chicken you'll likely encounter is found in the Garden of the Gods, behind a fire pit toward the end of the map

The second chicken you'll likely find, hidden in an apartment in the Sans Luxe Apartment building, accessible after the quest in the Garden of the Gods. Requires you to fix a generator or break the door down.

This Chicken is hidden in a closet in the Broadmoor heights Church, accessible after the Garden of the Gods situation is resolved. Requires you to use a switch on the wall in the church to open the door to the closet.

This is the only one that isn't accessible right at the beginning of the game, it requires you to have obtained the side quest Lords of War (it is automatically assigned to you a little ways into the main story)

After all chickens are present in your Ranger HQ chicken coop, all you have to do is wait and play the game. After the events in Aspen with Victory, you'll be called back to your HQ and then attacked, as this attack commences the chickens will assemble into Poultron and you'll have your achievement.