A couple of similar knives just ended on eBay a few days ago. Good prices too.
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=6528696909
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=6528696923
So far, all of the examples I have seen have come from British sources, which adds to the idea that they are WWII bring backs by British military forces stationed on the Cocos Keeling Islands during that period.
More pictures later.