z3c.repoexternals recursively retrieves subversion directory listings from the url or path and matches directories against a previous set of svn:externals if provided then against regular expressions and generates qualifying svn:externals lines. The defaults generate a set of svn:externals for all the trunks in a repository and keeps them up to date with the repository as new trunks are added when the previous externals are provided thereafter.

http://cheeseshop.python.org/pypi/z3c.repoexternals

Ross