A freindly source has suggested the item below, which I found is available in the UM-W music library, for a guide to underground 60's rock in Wisconsin. You might cross-reference this with what you find in some of the other sources to determine which bands could be considered activist. Then, armed with some names, you can head to your local used record stores, salvation army and/or other thrift shops, etc., in search of records.

The booklet:
Author: Tourville, Tom W.
Title: "They couldn't tame us" : the Wisconsin 60's rock discography / Tom W. Tourville.
Edition: 1st ed.
Publisher: Fairmont, Minn. : Midwest Publications, c1992.
Description: iii, 96 p. : ill. ; 28 cm.

Location: Music Library Wis. Music Archives-Ask Staff for Assistance
Catalog: UW Madison
Call Number: ML156.4 R6 T68 1992
Copy Number: 1
Status: Not Checked Out