You could also try searching for ISBN's on university domains, but I imagine this will be less consistent.
My university partnered with Barnes and Noble and published a list of required books per course as a bundle option. If a course catalog is available you can further refine your search based on course numbers (like FIN 4401 or CSE 4096, etc). Look for any partnerships a university has with a bookseller.
Those are some thoughts... good luck!
Emailing faculty or departments directly may offer (occasional) success, as can tracking down reader lists at campus bookstore websites.
There seems to have been a brief golden decade of roughly 2002--2012 when handcrafted professor homepages included course lists and syllabi at least at major universities, both public and private. It's grown markedly worse in recent years.
Open Courseware, under that name frequently, is an exception. M.I.T., Harvard, Stanford, and Cal Berkeley, off the top of my head. CUNY and Columbia likely as well.
For Stanford https://explorecourses.stanford.edu/
Across the bay, it's http://guide.berkeley.edu/courses/
Plugging in course numbers, restricted to domain, and keywords "syllabus", "assigned reading", or similar, often works. I'm not above emailing faculty or departments directly.
Readings, especialy in graduate courses, often comprise of articles rather than standard texts. For these, a course-specific reference (syllabus) is often necessary.
If you are interested in just a small number of courses just Googling it will surely tell you what the book is. But for a school-wide list the bookstore is probably the only option.
But remember, they are top schools usually in spite of, not because of, the textbook selection.
Untrue.
They may be, but the practice seems to be fading.
The "requirement" claim is rubbish regardless.
You'll see that there are weird code names for each course, and these can easily be found on the Courses page e.g. http://www.columbia.edu/cu/bulletin/uwb/
An example would be Department: COMS (Computer Science), Course: W3251, Section: 001
I'd imagine the case is similar for other colleges.
I think it only covers STEM subjects, which is unfortunate in your case. Still, maybe others on HN will find it useful.