@Alle,
I was thinking about how they'd found out about the bureau. Did they know about it from the moderator's group or did they just run into them somehow and think "hmm, sounds like a good gig." and start following them around?
To answer that. Okay, so I'm really bad at writing up like explanations of things? So, basically Mr. Giuseppe is this very powerful being that ran the bureau by himself before the current group did. He was getting on in years and as such needed successors. So he sent out a telepathic call to those he felt would be good fits. I.E children and teens who had begun discovering their powers and hadn't been turned evil by this (Secret) thing.
So think of it as the rogues, or strays from the main group had an instinct to go there. A thought in their own head that they needed to go there. So they all went there, some may not have joined or decided to only look from afar at the time, or some are just like "Yeah I'm not headed there yet." Lazys =_= but eh, it's like they already knew it existed. Now, normal people who aren't "super" only know about it when they're in dire need.
Um, hope that helped?? I'm really no good at explaining.. It kinda came with the powers that in the back of their minds they knew this place existed?