Patriot's Hangar
You can find this piece of evidence by following the walkthrough for the mission. From where you enter the hangar area, the evidence is in the far corner. You'll find a guard leaning nearby who doesn't move. You'll need to distract him to get the evidence.
Arena
The best way to get this is to dress up as the Patriot. You can find out how to do that in the walkthrough for this mission. Instead of going through the doors listed, however, go through the door that requires the keycard. If you haven't found the key card, go behind the Patriot's trailer and walk into the box maze. It will be on the ground to your left at the first turn.
These doors will bring you into the arena proper. Look up to find the glassed in VIP booth. Walk around the far side of the arena and walk behind the second bar you see. Go through the back rooms this way to get to the VIP booth and it will be on a table to your right from where you enter.
