SixA 0.1 codename "Pajitnov" is the latest (and first) "stable" release:
Click on this link to download the archive: http://edge.launchpad.net/gsixaxis/0.1/0.1/+download/sixa-0.1.tar.bz2

SixA 0.2 codename "Miyamoto" is under development, but you can download the latest branch using Bazaar:
$ bzr branch lp:gsixaxis

We do also have a repository, but it wont be in use until the release of SixA 0.2:
deb http://ppa.launchpad.net/sixa/ppa/ubuntu jaunty main
deb-src http://ppa.launchpad.net/sixa/ppa/ubuntu jaunty main