Hogan Archive of New Orleans Music at Tulane:
https://library.tulane.edu/locations/tusc/hogan-archive-new-orleans-music-new-orleans-jazz
RIPM Jazz Periodicals (contains full text to MANY jazz journals and magazines)
https://libraries.indiana.edu/databases/ripmjazz
Jazzinstitut Darmstadt:
https://www.jazzinstitut.de/en/
Institute of Jazz at Rutgers:
https://www.libraries.rutgers.edu/newark/visit-study/institute-jazz-studies
Library of congress: you can do a search for jazz (or other keywords) and limit results in a number of ways, including the facet “manuscript/mixed material”:
https://www.loc.gov/