The Swarthmore College and Community Store has an area set aside with textbooks for sale. They are organized by department and course number. Browse the shelves and make a list of what you would like to try to borrow. Besides taking note of a book's author and title, you will want to note the edition, the year of publication, and the name of the publisher. If the work is a translation, note the name of the translator. It's also useful to note the international standard book number (ISBN).
The Swarthmore College and Community Store offers a textbook search tool. If you are already registered for classes you can connect to a list generated in myswat. If not, you can browse by department and course. Once this tool generates a list, you can save a copy and use the information to look for library copies.
Not all professors interact with the bookstore concerning textbooks. Another way to learn about the books you need for a course before classes begin is to obtain a copy of the course syllabus. It is possible that your syllabus has been posted on a course webpage or in Swarthmore's course management software, moodle.swarthmore.edu.
Ask around to find someone who has already taken your class and can share an old syllabus with you but note that texts can change from semester to semester. Your student academic advisor can help. The professor of the class may also be happy to share a syllabus or textbook list with you. Contact information can be found in the campus directory or on departmental webpages.