You sure it's not kicking around in a tin can?
You have a lock that's not been in production for a very long time. Most people end up buying a few on eBay or wherever and cobbling a complete one together.
Some have purchased entire trailers, only to use just the door mechanism. Not trying to discourage you...just that you're probably not going to find a whole one somewhere, take parts as you find them and eventually you'll have what you need.
The " rest of the lock" is in between the door panels, you sure it's missing, not just behind the panel? I believe what you need is actually the L44 or L45 set up.