Well it should be found behind a locked door in Sabjorn's office in the meadery, if you on PC you could spawn one with the command -
player.additem 00019952 1
Nothing you can do on a PS3 and 360 if an item is missing.
Can you get it without picking the master lock?
What if you never got the quest to steal this, but you find it while doing the dampened spirits quest and it prompts you to take it to delvin? If you take it to him and get the money for it without getting a larceny quest for it first, will it screw something up later in the thieve's guild quest line?
I triedz taking it before reciving the quest andz it gives me an instant quest to return it, nothing special andz no bugs :D
What do you think?