You can use Worldcat to search for titles at libraries across the world.
If you find something that Swem doesn't own, you can request the item through interlibrary loan.
Useful subject headings for finding philosophy books in Swem's online catalog (this is just a small sample):
Philosophy, African
Philosophy, American
Philosphy, American -- 18th century
Philosophy, American -- 19th century
Philosophy, American -- 20th century
Philosophy, Ancient
Philosophy and cognitive science
Philosophy and religion
Philosophy and science
Philosophy, Asian
Philosophy, British
Philosophy, Buddhist
Philosophy, Chinese
Philosophy, Comparative
Philosophy, Confucian
Philosophy -- Early works to 1800
Philosophy, English
Philosophy, European
Philosophy, French
Philosophy, German
Philosophy, Hindu
Philosophy -- History
Philosophy, Indic
Philosophy -- Introductions
Philosophy, Islamic
Philosophy, Jewish
Philosophy, Marxist
Philosophy, Medieval
Philosophy, Modern
Philosophy of mind
Philosophy, Renaissance
Philosophy, Russian
Philosophy, Taoist