If you already know how to use Turbine and simply want the latest binaries or source, you can get them from the Apache Mirror System.
If you look for older releases of Turbine, both, binaries and source, you can get them from the Apache Archive.
You can check out the latest source from the Turbine Subversion repository. Information on connecting to the ASF Subversion repositories can be found on the version control page. More specific details can be found on the Source Repository page, within Project Reports under Project Documentation, of each Turbine sub-project.
svn checkout http://svn.apache.org/repos/asf/turbine/core/trunk/
Be sure and read the README.txt file for instructions on how to build Turbine. Turbine uses Maven as its build system, and building is as simple as running 'mvn package' at the top of the source directory.