I have lurked on this forum for a while. I saw the fellow who had a Type 99 brought back from Okinawa. I have a Type 99 bring back as well, but from Saipan. My great uncle was a naval aviator, who had the time of the invasion of Saipan was the Air Group Two (U.S.S Hornet, CV-12) commander. He led the close air support for the invasion landings of Saipan and Guam. I read through the cruise book and it states that the Hornet airmen picked up a number of souvenirs from Saipan, so that is how I deduced it came from there. No solid proof, but it was on an island he had said he flew CAS for the Marines landing, so I think I have a solid guess. He apparently got it from the Marines who appreciated the job he and his men did.
It is all numbers matching, the best I can tell. It is a Nagoya Series 4, with original sling. No bayonet, dust cover, but it does have the AA wings still intact.
Thank you for looking!