rec.games.corewar on Google - since it's formation in 1991, the newsgroup has provided a valuable forum.
The #COREWARS IRC channel on KOTH.org. Daily events have been logged since 14 Sep 2005 in KOTH.org's irc-logs directory.
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