What a coincidence! I acquired the same model as part of a collection sold five months ago It also had the pull string which worked well but I happened to have one spare Omron lock which worked out well. To find an original lock may cost more in the end.

Did you ever find a key? I have the same machine, and took the lock to a local locksmith and they told me $30 to make a new key.... any suggestions?
If you don't mind the lock that is there already then I agree with spending the $30. Keep in mind if it's some aftermarket type of key it may not turn left and right as originally designed. Turning left simply opens just the glass face to access the play field. You can easily do this from inside with the door opened. De-pining the lock is okay too.

All good ideas. It's all about how original you want it and at what cost.