The Bryn Mawr Rare Book Collection has extensive holdings for the 18th century. Librarians Eric Pumroy and Marianne Hansen have put together lists of relevant titles:
Books on London
Books Relating to 18th Century France 2006 [Titles in French]
They welcome researchers from Haverford. E-mail or phone them to tell them your research needs before going over to Special Collections, so that they can have things prepared for you.
The Rare Book and Manuscript Library at the University of Pennsylvania has holdings in 18th century printed materials that are indexed in the Franklin catalog. There are also some manuscript collections. See the library's <a href="http://www.library.upenn.edu/rbm/">website</a>.
Online and Print Collections of Primary Sources