The major Anderson discussions on USENET take place in newsgroups rec.arts.sf.tv and rec.arts.tv.uk . Discussions are infrequent; however, they do occur, so read the groups regularly if you have access and watch for them.
For more specific discussions, there are three Anderson listservers around. The oldest is the 1999 list, located at quack.kfu.com. An unmoderated list, it provides lively discussions with other 1999 fans round the world. Send an e-mail message with human-readable text (the list is not updated automatically) to This email address is being protected from spambots. You need JavaScript enabled to view it..
The info above is a bit out of date, so you might want to also try Yahoo groups, google groups and of course the TV21 forum! Check the RESOURCES page for more links!