Just got myself another NC30 and the seat lock is missing. Is there any way of getting it off without taking the rear fairing apart?

The pillion seat is unlocked via a cable from the lock mechanism behind the riders arse.. If the mechanism is gone you might still be able to hook the cable end thru the hole, otherwise taking the seat fairing off is only other way, but its not that much of a hassle

as said if its as it should be you should be able to just poke your finger in there and push the metal tab to the left to unlock it, if you cant undo that its a bit more difficult and you have to get your hand under the fairings (it is a hassle unles you have mini hands)