I was looking at the FBI archives and found a link some of you might like to scrape for information. I looked up the Weatherman's Underground and other extremist groups

https://www.fbi.gov/@@search?SearchableText=weathermans+underground&pageSize=20&page=1&sort_on=&sort_order=descending&after=&searchSite=vault.fbi.gov

All 6 parts of the Weatherman's underground and more

then from here: https://vault.fbi.gov/gangs-extremist-groups