As described on this Stackoverflow post on how to re-enable old repositories for unsupported Ubuntu releases, you have to edit
/etc/apt/sources.list and replace all occurrences of archive.ubuntu.com with old-releases.ubuntu.com.
However, for some reason, raring updates are nowhere to be found (at the time of this writing) under http://old-releases.ubuntu.com/releases/.
They are, however, somewhere else, namely http://old-releases.ubuntu.com/ubuntu/dists/. So I've managed to get things (i.e.
apt-get stuff) running again by replacing the old sources with the string
HEADS-UP This should be used only when upgrading to a newer OS version is not possible or otherwise not applicable. You will be using an outdated version of Ubuntu with potential security holes.
This is how the beginning of file
/etc/apt/sources.list looks like now:
# deb cdrom:[Ubuntu 13.04 _Raring Ringtail_ - Release i386 (20130424)]/ raring main restricted # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to # newer versions of the distribution. deb http://old-releases.ubuntu.com/ubuntu/ raring main restricted deb-src http://old-releases.ubuntu.com/ubuntu/ raring main restricted ## Major bug fix updates produced after the final release of the ## distribution. deb http://old-releases.ubuntu.com/ubuntu/ raring-updates main restricted deb-src http://old-releases.ubuntu.com/ubuntu/ raring-updates main restricted # FILE TRIMMED. OTHER SOURCES HAVE NOT BEEN INCLUDED