Japanese Law A-Z at the University of Washington Law School Library
You can look up the history of changes to particular laws in NDL’s Abolished Laws Database [日本法令索引廃止法令検索]:
Laws change over time, and it’s important to know which specific year you want to see. The law may have changed many times between 1910 and 1945, for example. Finding “snapshots” of a law for a given point in time can be done using print publications such as various versions of “roppo” (六法) . Roppo Zensho at Law Library (2014 - ).
University of Michigan Library has a number of these annual publications going back many years. Also, each law and it’s various amendments over the years are also separately published in both 法令全書 and 官報.
Historical Kanpō for the years 1883 (明治16)年7月2日 - 1952 (昭和27)年4月30日 is available in National Diet Library.
English gazzette Kanpō are available at the National Diet Library.
East Asian Law Library Resource in the U.S.
AALL FCIL (American Association of Law Libraries, Foreign, Comparative and International Law SIS)