This is not a definitive answer, but here are a few suggestions of groups that you can pursue. I found these organizations by crawling through the pages of larger women's organizations, particularly their "resources" sections.

• The Philadelphia Branch of the Women's International League for Peace and Freedom
• The Black Women In Sports Foundation, headquartered in Philadelphia
• Women's Law Project
• Philadelphia chapter of the National Organization for Women
• According to this webpage, there is a Philadelphia chapter of the Global Women's Strike
• Women's Way
• There are several student groups in Pennsylvania that participate in the Feminist Majority Foundation, including one at Swarthmore
• The Philly gay calendar might also lead to other possibilities
• I'm not sure if these groups would be considered radical, but Feminist.com lists several anti-violence organizations in Philadelphia