In the Library catalog and databases, try a variety of subjects and keywords to find more materials. If you're looking for a specific subject (abortion, gay marriage, prayer in the public schools, etc.), you can add the terms "Law and legislation" or "Religious aspects" to narrow your search. Some common subject headings are
Church and state ---- Christianity [Islam, Buddhism, etc.] and justice ---- Christianity [Islam, Buddhism, etc.] and law
Freedom of religion ---- Religion and law ---- Religion in the workplace ---- Religious discrimination
The Library has hundreds of e-books on this topic; this is only a representative sample to give you some ideas. Please use the Library catalog to find more books. Ask a librarian if you need help.