Currently there is just the one official forum, however various of the organisations planning on playing PfO have their own role playing forums. See Nihimons helpful guide thread for details also there may be opportunities for rp on the PfOFan forum which is cross organisation.
Other opportunities may arise by just getting to know a few of the community members.
I can certainly confirm that Aeturnum has role play forums Role play forums for Pax but we are certainly not the only such organisation out there