I found it at the reception desk,right outside the room that requires it.

After passing Nikolai's trap you will eventually come to the reception desk area that def2ll had mentioned. After approaching the desk the two doors on either side will open. Kill the zombies and then walk through either of the two doors, turn towards the center of the the wall (to the right if you go in left doors, and your left if you go through right doors) go into the small room and the key will be in a basket on the right wall of the room.

There is a small room in the middle of the area where the black keycard is, its kinda hard to find with all the zombies around so take them out first. Once you do just go to the door where the objective is, turn around, and walk forward until you eventually see a door on your left side (<<<) inside is where the black keycard waits.