I can think of two sources you can check.

The Freedom Archives contains over 8000 hours of audiotapes. These recordings date from the late-60s to the mid-90s and chronicle the progressive history of the Bay Area, the United States, and international solidarity movements. The collection includes weekly news/ poetry/ music programs broadcast on several educational radio stations; in-depth interviews and reports on social and cultural issues; diverse activist voices; original and recorded music, poetry, original sound collages; and an extensive La Raza collection. Programs and clips are downloadable.
The Freedom Archives

The Social Activism Sound Recording Project is a cooperative endeavor developed by radio station KPFA-FM (Berkeley, California), the Pacifica Radio Archives (PRA)(Los Angeles, and the UC Berkeley Library. The goal of the project is to make accessible via the web a unique library of recordings of significant people and events that shaped the politics and culture of the 1960's. The first phase of this project focusses specifically on social activist movements in Berkeley, California, particularly the Free Speech Movement.
The Social Activism Sound Recording Project