There were caves on the coast of Tinian to be sure. After the Silverplate squadron arrived (the boys who dropped the bombs on Hiroshima and Nagasaki), they were still finding Japanese soldiers encamped in said caves. Finding a Type 99 in a cave would not be out of the question... but I would think they would have also found an enemy soldier holding on to it! Some of the Japanese soldiers that held post in remote locations never got the word that their divisions had left, or even in some cases, that the war had ended, and they would have continued to hold that post and fight with their lives until dead, or until word finally reached them. One of the interesting thing about the Japanese back then: they simply did not give up even when they had lost the battle/war!