A list of mephisto repositories can be found here:

http://static.saga.cct.lsu.edu/mephisto/repository/

You can use the --repository= option to list the
content of a certain repository:

perl mephisto.pl list --repository=1_5

and to force the installation of a certain repository
version:

perl mephisto.pl install –target-dir=/opt/saga/ --repository=1_5