etckeeper is available in git at git://git.joeyh.name/etckeeper, or
in gitweb.
It's packaged in Debian, Ubuntu, Fedora, etc.
Or, you can install it by hand. Before running 'make install', you should edit etckeeper.conf and make sure it configured appropriately for your distribution.
Distribution packagers may find it more convenient to set CONFFILE to point to a different etckeeper.conf that is preconfigured for your distribution.