Tina Modotti, Woman from Tehuantepec, circa 1929 (Source: Wikimedia Commons, Public domain)
Primary sources that have been edited, reprinted in facsimiles, or transferred to microfilm can be borrowed through Interlibrary Loan if they are not in Tripod. Many of them will be listed in Tripod or WorldCat under subject terms and such words as "sources", "correspondence", "personal narrative*", or "memoir*". For example, the search mexico history sources produces books including:
Books printed in earlier time periods are kept in libraries' rare book collections. You can go to Haverford's Special Collections to see materials.