haven't found them all but maybe this will help.
1. Found after leaving station going into chinatown. Found right in front of steps.
2. Found in Grinder's lane apartment area. Part of the side quest to cap a squealer. Enter room and it's hanging on the wall.
3. Found in the building across from Shroute's apartment. Use creeping dark to get in the window to enter the room to kill the guy and grab the costume on the wall. This is part of Vinny's hit list quest. If I remember right, it's the last one on that list.
4. Found in central subway station in the abadon subway car.
5. Found by helping a girl get her keys back from her no good boyfriend that took over her apartment. Hanging on the back wall. Side quest takes place after the second visit to ww1 era.
6. Dial 4263
damn nice all I have is the potato sack suit one right now lol