We've not made a release since forking off, but you can download tarballs of the last release from the (now frozen) original snowball website.
We provide and support python wrappers for Snowball. The latest code can be downloaded from the PyStemmer repo.
Developers may wish to access the latest source using the command:
git clone firstname.lastname@example.org:snowballstem/snowball.git
The git repository can also be browsed online.