>>106898723I use Aussie, personally, but it might depend on the hair. /fa/ might be helpful.
As for pick-up lines, try to think of in-jokes relating to what she's cosplaying as. If she doesn't catch their meaning, then you can start a solid conversation explaining it, but be sure to keep your tone light and don't accidentally sound condescending. If she does catch the meaning, follow up with saying something like, "I've used that joke on a couple of others and you're the first one to catch it."
Whether she's alone or in a group---most likely the latter---you could say either that you're new to the convention scene and could use a guide, or if you're not new, just say that you can't ever convince your friends to join you at conventions and ask if you could join their mob.
Bear in mind, of course, that you're probably not going to get lucky on your first, or even fifth, try, especially since attractive girls are almost always in a committed relationship, regardless of how coo coo for CoCoPuffs they are, but that's fine; you'll probably need some time to practice, anyway.
