I made an nice discovery this weekend. Certainly for all of Kyushu and probably for all of Japan there are books available for the private fishermen detailing decent fishing sites. They consist of aerial photographs of the coastline which also show some of the underwater topography quite well. They have information about the sites including how to get to them etc. The one I bought tonight for Fukuoka province was 4000 yen and has given me a really good way to identify potential dive sites in my local area.