There are plenty of mature PvPers. The problem you're facing, is the problem almost everyone has when they're looking for a pickup group; The majority of players who have no group, are extremely immature.
Here are a few suggestions and observations that I hope will help you:
1) Build a friends list. Everyone that you meet that's mature, willing to group, and a good player or willing to learn, add them to friends.
After awhile, you'll find that you can always build a team using only players from your friends list, and when you can't, you'll find your friends usually have other mature friends that can come. Or, at the very worst you might have to take 1-2 pickups, which certainly isn't as bad as a team full of pickups.
As odd as this may sound sound, PvP is just as much about social skills as it is about player skill and teamwork.
2) Find a guild. I'd advise against joining any guild that's advertising in local chat, as most of these guilds tend to not be serious PvP guilds, are highly inactive, have extremely immature leaders/officers/members, or are simply whacked out in some other way. I recommend only joining a guild where you already know some of the members(friends list ftw). This can land you in some great, serious guilds with mature members.
3) When you do PUG, try to form your own group. This way, when you have the guy who joins the group, logs on vent and screams "z0mg w0manz!1!!!" very ecstatically on Vent, or simply won't listen to anyone, you can kick them. Make sure to interview members, the best way to do this is instead of having a "Self-invite" policy, have a whisper for information policy when advertising. Make sure to ask them questions like; "What can you play?", "What are you currently rolled as?" "Can you play a/an *insert build* with *insert skills and attributes*?".
Make sure you know what build you want to play, and what skills and attributes everyone should have, before starting a PUG. When the players are finished rolling, inform them of their general role. Alot of people might already know it, but some may not. If you're going with a full PUG, try to pick a simple build, that doesn't require alot of teamwork or multi-tasking.
4) Never openly advertise personal information. It may be (very) important to you, but your average stranger doesn't care, and your average 10-year-old will hassle you about it until you put them on ignore.
5) The Gladiator's Arena fourms here are a great source of information. If you ever have a question about something in PvP, such as a build, tactic, or anything else, I recommend you post there about it(make sure to search first though). I'd also recommend you check out
www.team-iq.net which is another excellent source of information on PvP.