The upside to this big disappointment is that they WILL hold a spot for you.
Note: Remember how you felt about doing DBT a little while ago? Take a look at where you are now. Originally you were hesitant about DBT and now you're in action and taking steps to get the ball rolling. I LOVE the motivation and commitment you have right now. Don't let the disappointment of not getting into the group right away make you lose that motivation and commitment.

You have momentum (though it might feel a bit waned at this point in time). Use that momentum and be proactive. As others have mentioned, there are DBT handouts and self-help guide type things all over the place. You also have the handouts that you previously used. Take advantage of this big chunk of time before the group begins: Whip those handouts out of hiding and start getting yourself familiar with the modules, acronyms, skills, etc. By the time you start the group you will be way ahead of the game.

Time really does fly. October will be here before you know it. And you've got your PC community to help support you until then