There are only scattered fragments, but key seems to be Saburo Sakai's statement in his book that U. S. Navy PBYs of Patrol Wing TEN, U.S. Asiatic Fleet, had made several overflights of Japanese air bases in southern Formosa in the weeks just before the beginning of the war. Predictably, nothing in USN records supports this. Several have told me that a document in the Pearl Harbor Investigation papers is a diplomatic complaint by the Japanese about precisely these overflights, but I have yet to find it. Anybody with clues or tips, please pass them on.
1941, Chronology with documents You may find what you're looking for here. Or you can try The "Magic" Background To Pearl Harbor
Not much help for you, but I have several recce photos taken of airbases in Taiwan (Formosa) in Jan 1945. Interested?
New Answer for you: December 8, 1941: MacArthur's Pearl ... - William H. Bartsch - Google See Chapter 8.
New Answer for you:<br><a href="http://books.google.com.tw/books?id=r8PutH7_T2gC&pg=PA237&lpg=PA237&dq=1941,+Formosa,+reconnaissance&source=bl&ots=0jD4vo9XYi&sig=MUDUX7N8CYFmkFFXNkiLqa9QKYM&hl=zh-TW&ei=BsWJTtWmCIiKmQWRg7wR&sa=X&oi=book_result&ct=result&resnum=1&ved=0CB4Q6AEwAA#v=onepage&q=1941%2C Formosa%2C reconnaissance&f=false">December 8, 1941: MacArthur's Pearl ... - William H. Bartsch - Google Formosa%2C reconnaissance&f=false</a><br><br> See Chapter 8 pp 230-240.