Use the Tripod catalog to look for relevant books owned by Haverford, Bryn Mawr and Swarthmore.
Use WorldCat to find books not held by the tri-college libraries.
Doctoral students go through an exhaustive literature search when writing their dissertations. They also tend to work on new questions, sometimes ones that have received very little attention from scholars before. You can obtain many of these dissertations and benefit from all the bibliographic treasues and new ideas. Check ProQuest Dissertations & Theses to identify dissertations on your topic.