Goto michaelkors.com to retrieve the customer service # and just call and advise you losr the lock, they will ask for serial # to authenticate, but as long as its authentic they will send you a new lock! Good luck
Just a word of caution. I recently contacted MK for a replacement logo charm. I had to send the bag in. And when I got it back, they put a metal charm on the bag instead of the original leather charm and I had to send it to them AGAIN. All at my own expense. Just be prepared, because this might happen to you as well.