Que raro que no te aparezca, yo uso kubuntu y este utiliza como administrador de paquetes el Adept y asi es como tengo la lista de repositorios /etc/apt/sources.list
Código:
deb http://mx.archive.ubuntu.com/ubuntu/ hardy main restricted
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy main restricted
deb http://mx.archive.ubuntu.com/ubuntu/ hardy-updates main restricted
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy-updates main restricted
deb http://mx.archive.ubuntu.com/ubuntu/ hardy universe
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy universe
deb http://mx.archive.ubuntu.com/ubuntu/ hardy-updates universe
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy-updates universe
deb http://mx.archive.ubuntu.com/ubuntu/ hardy multiverse
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy multiverse
deb http://mx.archive.ubuntu.com/ubuntu/ hardy-updates multiverse
deb-src http://mx.archive.ubuntu.com/ubuntu/ hardy-updates multiverse
deb http://archive.canonical.com/ubuntu hardy partner
deb-src http://archive.canonical.com/ubuntu hardy partner
deb http://security.ubuntu.com/ubuntu hardy-security main restricted
deb-src http://security.ubuntu.com/ubuntu hardy-security main restricted
deb http://security.ubuntu.com/ubuntu hardy-security universe
deb-src http://security.ubuntu.com/ubuntu hardy-security universe
deb http://security.ubuntu.com/ubuntu hardy-security multiverse
deb-src http://security.ubuntu.com/ubuntu hardy-security multiverse
Checa como lo tengo
http://bp1.blogger.com/_4JelGwxTmeM/SGGiA92L9hI/AAAAAAAAAAc/v2IkF2wvvhE/s1600-h/instant%C3%A1nea1.png