The Arc's Criminal Justice initiative is working to ensure safe, fair and just treatment of neurodiverse individuals and people with intellectual and developmental disabilities when interacting with the criminal justice system. See the section How You Can Help for ways to contribute.
The Prison Policy Initiative provides an advocacy toolkit for anyone working to reform the prison system in the US. Worth Rises also has a Take Action section that they regularly update with new prison reform campaigns.
The Association for Autism and Neurodiversity runs regular free online sessions to connect with other autistic people or parents of autistic people.