mod_openpgp's source code, along with the maotest.buanzo.org test site and (in the future, ehem) some tools are stored in buanzo.org's Subversion server.
You can check out the source tree with this command:
svn checkout svn://svn.buanzo.org/mod_openpgp
It will create a subdirectory called "mod_openpgp" in the current directory. From then on, you can just issue an update command:
cd /path/to/mod_openpgp svn update
If you have patches, or want developer commit access, mail me at buanzo [AT] buanzo [DOT] com [DOT] ar.