The complete source code is available from the JabXPCOM repository. You can either use the official CVS repository at http://cvs.sunsite.dk/viewcvs.cgi/jabxpcom/
or the bleeding-edge Subversion repository at http://svn.cmeerw.net/src/jabxpcom.
JabRSS itself consists of the files jabrss/jabrss.py and jabrss/parserss.py,
but you will also need a working JabXPCOM installation.