Find a good secondary source (book, article), and mine its bibliography. Look for primary sources and types of primary sources used to create the secondary source.
Use sources to find: synonyms/contemporary terms - people's names - place names - dates - distinctive quotations and phrases that will lead you to further sources via databases and Google Books.
Use Google Books Advanced search to find key phrases such as names or dates or event names in books written during a certain period and/or with a certain word in the book title, and/or by a certain author
Use the C19 database. There's no full text here, but many articles indexed here are held at the MU Libraries. Check the MERLIN catalog to see where, and in what format, we own the periodicals - use the Journal Title search in MERLIN. They may be available in print (in Ellis Library or requestable from the Depository), or they may be on microfilm. The Parliamentary Papers can also be searched from C19.