Just ending this thread.
The locksmith finally gave up trying to find a replacement key cylinder for my lock. He did manage to find a cabinet lock that was the same diameter but had a shorter barrel. With a little machining he adapted the cabinet lock to work with my lock. $50.00 later and all is good.
FYI Use a good silicone 3in1 spray to lubricate the lever mechanism. You can get to this by pulling off the back plate and also squirting the bolt action. Use a dry graphite for the lock cylinder assembly, as it won't attract dust, which attracts moisture.
He mentioned that this lock is a great lock with yearly maintenance and is light years better quality than todays RV locks.