Sources
You can find the sources of the latest release on GitHub.
Binary
po4a is a Perl module. It is available as a binary package in many OpenSource distributions (Debian, Ubuntu, FreeBSD, Gentoo, Fedora, Mandriva, and probably others).
Git repository
The latest sources are available from our Git repository.
It also contains additional modules which are being considered, but are not of sufficient quality to be released yet. In other words, they are still waiting for your contributions :)