You can check all the guild information online.
http://www.camelotherald.com/newfrontiers/
Click on your server, and then you can check out all the guilds that are doing well in rvr.
Then you can contact the one you are interested in by either contacting someone from that guild in game by /who "guild name" and sending /send message or by checking out the guild website and posting a application.
Hope this helps. =P