WorldCat.org lets you search the collections of libraries in your community and thousands more around the world. WorldCat grows every day thanks to the efforts of librarians and other information professionals.
NOTE: Type in your search term(s). Once results arrive you can narrow your search to "archival material" as indicated in the image below. This will help return results that might be primary source materials.
https://beta.worldcat.org/archivegrid/
ArchiveGrid includes over four million records describing archival materials, bringing together information about historical documents, personal papers, family histories, and more. With over 1,000 different archival institutions represented, ArchiveGrid helps researchers looking for primary source materials held in archives, libraries, museums and historical societies.