Look under your candidate's name as author. This search will retrieve whole books containing published diaries, correspondence, memorrs, and autobiographies written by your candidate. Examples:
These same strategies will work in the WorldCat catalog of libraries worldwide. Published books you find in WorldCat can usually be requested on Interlibrary Loan (ILLiad).
Scholarly reference sources, such as American National Biography, will list for you works by your candidate, as well as listed published works about them.