I think Gilgamesh used to be the secondary unofficial RP server but I'm not so sure RP is big there anymore, I definitely never saw any going on when I was leveling a character there. If you're wanting RP to be big and ever-present I think you're gonna have a hard time finding it somewhere other than Balmung sadly! You might make a character on Gilgamesh and give it a try, maybe there's a RP FC you'd fit in with.

Good luck!