Jim,
which one of the three keys did you loose?
If it is the ignition key then you only have two options since the ignition lock is NLA.
1. There is a used lock for sale on eBay, but you better sit down before you read the price!
eBay: 120562087460
and I believe BABAK has one for sale too.
2. Remove the chrome cap by drilling out two posts (rivets?) to get access to the tumbler and bring it to a lock smith.
Al Lieffring described how he solved the problem here:
http://www.sl113.org/forums/index.php?topic=10296And here is a description in German how to do this. The group there looked into the possibility of reproducing them but the costs are prohibitive.
The info also mentions that a "KeyProf Luke" in Holland will repair your lock for quite a bit less than the what you pay for a complete used one.
Might be useful to send him an inquiry.
http://www.keyprof.com/en.Product-Slot-Revisie.phpGood luck!