Hall of Heroes - under the desk in the ticket office, near the entrance to the building.
Hall of Heroes - in a side room visited along the way to the exhibit.
Hall of Heroes - under the statue's feet in a side room visited along the way to the exhibit.
Wounded Knee Exhibit - near the Fireman's corpse in the main part of the exhibit.
Peking Exhibit - inside a room reserved only for the employees.
Peking Exhibit - behind a gong in the corridor leading to the main part of the exhibit.
The Courtyard - in a dark corner of a small warehouse on the ground floor (you can explore it after the battle with Slate's men).