I might start here at the Figaro server forums. There are linkshell ads in there.

But honestly, the easiest way to get into a linkshell is to just party with people in the game. If you see someone running leves at your camp, offer to party up for the leves. If you see people grinding mobs, offer to party up. Party up for behests.

Most people are in Uldah, so if you're looking for people, you might want to go there. I've seen people in Uldah shouting for Linkshells and parties. So that could be a way to go.

Good luck!