Option 1: It's usually wise to start with secondary sources (books, articles, etc.) or tertiary sources (encyclopedias) that will lead you to specific laws and cases, which will be neatly cited in the footnotes or the bibliography. Let an historian do some of the legwork for you.
Option 2: Newspapers will often give a play-by-play of a major case; newspapers of record will make the public aware of a new law.
Once you know what law or case you need, search WestLaw Next