Don't hestitate to contact law librarian Michelle Penn if you have any questions about accessing library resources.
Gale's The Making of Modern Law: Legal Treatises has more than 21,000 Anglo-American legal works published from 1800-1926.
While searching with the Making of Modern Law: Legal Treatises and HeinOnline's Legal Classics library are likely to be the most fruitful resources for finding historical treatises you may also want to check the free resource HathiTrust and the Library's OneSearch. You may also wish to look at LLMC, which besides treatises, contains select historical statutes, case reporters, newspapers, and other resources.