rec.games.corewar on Google - since it's formation in 1991, the newsgroup has provided a valuable forum.
ICC 2004 - the 20th Anniversary of Corewar Meeting organised in Berlin by Christian Schmidt, July 2004.
Jakub's IRC Logs - old logs of the happenings in #COREWARS covering the period Mar 2003 to May 2004.
Corewar Web-Forum [use rec.games.corewar instead]
Koth has a mailing list echoing rec.games.corewar. To subscribe, send an email to firstname.lastname@example.org with a body of subscribe corewar-l (name).