The best ways to find archives are to:
In the print collection, we also have published guides like:
In truth, print guides have fallen out of fashion, especially with the development of Worldcat and ArchivesGrid
In WorldCat, search as you normally would, then in the results page limit to the "archival" tab. Click on the "Libraries worldwide" tab to indicate where the materials are held. The record should also indicate whether microfilm scans of the material are available. This will help you find individual letters/materials in archives.
This works even better if you subject search, which will point you toward whole collections. Start with keywords first, then move to subjects or title search if you need to limit the results.
Like Worldcat, this database is owned by OCLC (Formerly "Online Computer Library Center," and before that "Ohio College Library Center").
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Cons:
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