The National Institute for Informatics (formerly NACSIS-National Center for Science Information Systems) maintains a website with pages in English and Japanese.  Links below are to the English versions.

The NACSIS WEB CAT can be searched online.  If you want to view the data with Japanese characters, set your browser to view the UTF-8 character set (fonts must be loaded onto your computer for this to work).  If you don't read Japanese, this will do little good; it serves just as well to see iin English any data that is in English and see little boxes where there would normally be Japanese characters, which is how it comes up if you view it using an English language character set. .

If you can get a hit, click on it and you will get a full entry (again with only English characters and small boxes displaying unless you have UTF-8 viewing capability) and holding libraries.  The listing for holding libraries is in Japanese (boxes) so that is not much help initially, but don't give up.   A click on any of them will give you holding libraries, with the names in English as well as Japanese (boxes).

There is a NACSIS-ILL page that implies an Interlibrary Loan component, but it is not one I understand.  It appears that if you are a member library, you can process the request while in the catalog.   I suspect that the member libraries are the Japanese Libraries and that this is for ILL within the country, but perhaps someday it will expand to be international in scope.

It indicates the ILL catalog contains a gateway to the National Diet Library and the BLDSC.

The National Diet Library  This site has information about the library, as well as a link to the OPAC (bottom right of screen).  At first glance it appears to me that serials are not included in the NDL OPAC, although this seems unlikely.  The information pages include a User Guide and within that page is a link to International Services.   This page will give information on obtaining photocopies and loans from the National Diet Library.

BLDSC.   The BLDSC site won't allow links to individual pages, so once there, go to Collections, then Oriental and India Office, then Japanese for informaiton on their Japanese Collection.   Once on that page, note especially the link to Catalogs, which at first appears to be a listing of paper catalogs. Scroll down to find a link to the UK Union Catalogue of Japanese Books and Serials.

Bridge to Japan's Library catalogs with significant holdings of Japanese material

Japanese Info has title and publisher information for about 500 titles.

ARL's Japan Journal Access Project

Infonetwork  an information brokerage firm specialized in obtaining Japanese information to the US as well as to other countries throughout the world.

JASCI  (Japan Association for International Chemical Information) will supply a photocopy of any Japanese patent or other scientific and technical article.