The Duct recorder is an audio artifact in the Left Behind DLC chapter The Enemy of My Enemy. It is in the air duct passage on the left that Ellie crawls through after the fight with the hunters, next to a body.
Ellis, freezing in the duct, records his last message as the only member of his crew still alive.
He believed Regan was about to kill him when she reached for her gun, so he shot her first and ran. Fighting his way past infected tore open the stitches on his stump, and with one arm he cannot close the wound. He bleeds out in the duct.
Crew photo
The Crew photo is an artifact in the Left Behind DLC chapter The Enemy of My Enemy. After Ellie leaves the helicopter, look in the corner of a dark room shortly before the hostile survivors show up; it is on a decaying body.
Medical supplies
The Medical supplies artifact is the suture kit Ellie came to the Colorado mall for in the Left Behind DLC. She takes it inside the crashed military helicopter at the start of The Enemy of My Enemy and packs it for Joel.
Atrium note
The Atrium note is an artifact in the Left Behind DLC chapter So Close, set in the present-day Colorado mall. It is in the atrium, to the left of where Joel and Callus are hidden, near the remains of a field surgery.
Atrium recorder
The Atrium recorder is an audio artifact in the Left Behind DLC chapter So Close. It is in the tent near the crashed helicopter on the mall's upper level, the spot Ellie has been trying to reach all chapter.