To find some of the communication related to the anti-Prop 21 movement, you can search online. Through Google Groups, you can find email list and discussion board messages. I searched "proposition 21" OR "prop 21" and got 620 messages.

There are also organizations you may want to contact to see about getting a hold of protest flyers and other contemporary resources:

The Books Not Bars campaign of the Ella Baker Center works on issues of youth and crime and punishment (I tried emailing the project coordinator with your question but never received a response; you may want to call them).

The Pacific Juvenile Defender Center has relevant information on their website. There are Prop 21 updates in their Fall 2001 Action Alert, and you may also want to look at their "easy-to-read" Guide to Proposition 21.

The prison abolition group Critical Resistance has an Oakland chapter.

Another librarian familiar with criminal justice issues suggested the American Friends Service Committee's Pacific Mountain Region chapter and California Prison Focus as well.