If you've been ritualistically picking up the collectibles in every area, you'll get this at the end of the Oops Hardline mission.
There's a few that require having clearence to get to them.
On your way through, you'll notice doors with 1 on them. You need to meet Emily and then get the access 1 card to open this door and others around the map.
Once you've done the phone, if you still don't have it, don't talk to Emily, just double back and check these rooms are all open before going on.
Some spawn inside the Saferooms too, so make sure you open all of them.