The Guide to the ALM Thesis is the primary resource for Harvard Extension School degree candidates seeking to create an original thesis in their field of study.
From the above link, to search within the DCE theses collection, under the search box change the option to search "This Collection" and enter your search words.
ALM Theses in Harvard Archives
Older copies (currently, all copies prior to 2016) are available in the Harvard Archives, and are listed in HOLLIS.