Perhaps one or more of these organizations would have info about songs used in Juneteenth celebrations: http://www.juneteenth.com/orgs.htm

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June 20, 2021: These are in view via the Internet Archive Wayback Machine but there is no telling if any of it is still accurate: https://web.archive.org/web/20030205061808/http://www.juneteenth.com/orgs.htm