The source code is managed in a subversion repository at my own server. The address consists of https://svn.grrrr.org/ext/trunk appended by the respective external/project name (flext, pool, py, xsample, dynext etc.) and a trailing slash (/). Hence, flext is e.g. downloadable anonymously from https://svn.grrrr.org/ext/trunk/flext/ . For instructions on how to use subversion you can go here.

You can also look into the project pages at http://puredata.info/Members/thomas for detailed info on each external.