Best Coupler Lock? (help a newbie!)

Hi everyone. I am looking to get a coupler lock for my new AS Flying Cloud. I have a pin-type lock that goes through the hole on the coupler, but I would like something more secure instead (looks like a simple bolt cutter would take care of that). I understand there are some coupler locks that are made just for AS, or at least fit them appropriately. The dealer thought there was a specific coupler lock for AS, and ordered it for me from the AS HQ...however, when I got to the AS HQ and Service Center to pick it up, they said they can no longer get that part. Can someone direct me to the best coupler lock for an AS and where to order it? I want to protect my investment! Thanks!