cpanm --look Math::Pari
download ftp://megrez.math.u-bordeaux.fr/pub/pari/unix/OLD/pari-2.1.7.tgz manually into that directory, complete the installation by running:
tar -xvf pari-2.1.7.tgz perl Makefile.PL make make test sudo make install exit
If you encounter problems with this, again provide the output.
When this manual installation of Math::Pari is successful, then you can attempt the Net::SSH::Perl installation again.