ed will probably be able to give you a better description, but I'll do my best. :)
Head to the Southern area of the Armoury where you fought
(SPOILER)Revolver Ocelot. South of the main room is a small passageway. Keep heading right along this until you reach a wall, which upon examination is easy to bypass with help from some handy C4 explosives.
Having blown this wall open you'll reveal a small room, monitored by two gun cameras and with two doors at either end. The door blocking the room with the camera requires a Level 6 Keycard, so make sure you have that beforehand. I can't remember which door conceals the camera, but it shouldn't be too much hassle to check both.
To evade the gun cameras, chuck in a chaff grenade. Then dash into each room and collect the items inside. The camera should be in there somewhere. Best of luck finding it!