I can only speak about Remoting discovery mechanisms, but there is something that might work for you. Remoting has multicast and JNDI detectors that can inform a registered listener of known servers. See Sections "3.1. Discovery", "5.3. Discovery (Detectors)" and "10.4. Discovery and invocation" of the Remoting Guide (http://labs.jboss.com/jbossremoting/docs/guide/index.html) for more information.
You might also want to post a query on the "Installation, Configuration, and DEPLOYMENT forum (http://www.jboss.com/index.html?module=bb&op=viewforum&f=61) to see if there are other non-Remoting mechanisms that would work for you.