There was a Subversion repository for Tkabber's development source code on http://svn.xmpp.ru/repos/tkabber/. Tkabber development code was initially hosted on JabberStudio's CVS. On 16th August, 2006, it migrated to XMPP.ru's SVN.
As for now, Tkabber development continues using Fossil, so links presented here are either discontinued or don't update anymore.
This command downloads Tkabber to a directory called tkabber-svn:
svn co http://svn.xmpp.ru/repos/tkabber/trunk/tkabber tkabber-svn
Additionally, you can download tkabber-plugins to the directory tkabber-plugins-svn with this command:
svn co http://svn.xmpp.ru/repos/tkabber/trunk/tkabber-plugins tkabber-plugins-svn
For more information about the installation process, check the tutorial Installing Tkabber and dependencies.
There is also a Subversion repository for Tkabber's 3rd-party development source code on https://svn.xmpp.ru/repos/tkabber-3rd-party/. This command downloads 3rd party code to a directory called tkabber-3rd:
svn co https://svn.xmpp.ru/repos/tkabber-3rd-party/trunk/ tkabber-3rd
To get instant emails when changes are submitted to any of the above SVN repositories, you can subscribe to this mailing list: tkabber-dev