If you can locate an archive or library with original sources that interest you, you may be able to request digitized copies.
These four databases enable you to find specific archival and manuscript collections. They overlap, but each contains unique material.
Archive Finder -- an online database of archival materials in the US, UK, and Ireland
WorldCat -- in the Advanced Search, under "Limit Type To," select Archival Materials. Alternatively, under "Subtype Limits," choose Manuscript as the format.
Archive Grid -- a database containing all the archival and manuscript records in WorldCat (except dissertations), along with thousands of finding aids
Social Networks and Archival Context Project (SNAC)
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