A new database is now available. Nihon Gaiko Monjo (Documents on Japanese Foreign Policy) is a multi-volume set of publications detailing Japanese foreign policy since the Meiji era (1867 onwards).
The content is now being digitised by the Ministry of Foreign Affairs (Gaimusho), and is being made freely available as The Digital Archive of the Documents on Japanese Foreign Policy.
The database is not yet complete, with content currently available up to the end of the Taisho era (1926). To view the images in the database, you must download the free browser plugin DjVu which is also available via a link to the Caminova site given at the bottom of the title page.