To search through physical materials, it is good to familiarize yourself with the Library of Congress classification system, found here.
Call numbers JQ1499-1749 (J is the broader political science category, JQ is political institutions in Asia) will host a variety of East Asian political science resources. Subclass DS contains Asian history materials. These are good places to start your search.
To search through physical materials online, go to the UCLA library search page, and click on the three dots to navigate to the "Browse" section, and then select "Browse by call number". Or, just click here and enter your call number into the search field.
This collection contains materials that were censored during the occupation of Japan. There will be a demonstration of how to access and view microfilms.
Japan Times Archives: https://jt-archives.jp/authenticate.do
Toyo Keizai Digital Content Library: https://japanknowledge.com/lib/en/shelf/toyokeizai/
Japan Digital Archives Center: http://j-dac.jp/top/eng/index.html
The World And Japan (National Graduate Institute for Policy Studies): https://worldjpn.net/front-ENG.shtml
J-Global (database): https://jglobal.jst.go.jp/en
Hoover Institute (focus on modern history): https://www.hoover.org/library-archives/collections/japan
Japanese Law: https://liblawuw.libguides.com/japan-az
Japanese Political Science Association: https://www.jpsa-web.org/english/?l=en_US
Below are some bibliographies that may aid you in your search.
Below are some databases that offer either bi-lingual or English resources on Japanese academic subjects.