While it's true that Balmung and Gilgamesh are the worlds that have the largest RP communities, the RPC certainly wouldn't object to you using their site to try and seek out RPers on other servers as well! There are likely a few folks who would be interested in RP on every server, I'd think!

Anyway! I wish you luck in your search for a RP group to call your own! If you want to check out the RPC's site, they can be found at ffxiv-roleplayers.com!