The only thing I can suggest is you contact some of the independent parts suppliers like Motorworks, or James Sherlock or Motobins. They may have a second hand one on a damaged case.
Failing That, it might be worth a gamble buying a lock from the earlier cases fitted to the K series. The keys and key barrels are different, but the catch is a similar style and you may, depending on your skill level be able to make a functioning catch mechanism with parts from both catches.
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