Mishcon de Reya have an email address for anyone wishing to support the legal challenge to Article 50
Anyone wishing to support the action to ensure that the UK Constitution is upheld in this process should email Article50@mishcon.com.
http://www.mishcon.com/news/firm_news/article_50_process_on_brexit_faces_legal_challenge_to_ensure_parliamentary_involvement_07_2016#.V3lRaW3BuTM.facebook