This is easy peasy:
-s file:///export/home/pkgserv/reposource \
-d file:///export/home/pkgserv/repodest 'pkg:/*'
Be sure to set TMPDIR, as /tmp is normally RAM and this process can use an awful lot of disk space.
Rich Lowe has also mentioned the following tool, unsure if this is helpful:
python2.6 path/to/pkg/gate/src/util/publish/merge.py -r \
-d repo_merge \
-v true,http://localhost:13000 \
-v false,http://localhost:13001 \