MagicBand accessories and charms were first reported in early spring. There's many rumors out there regarding what exactly will be available for purchase, but you can feel confident that there will be plenty of options once the bands are available to everyone.
I first wrote about this in March:
http://blog.wdwinfo.com/2013/03/02/disney-magicband-styles-begin-to-surface/
Even since then, more rumors have surfaced. Now that we can see the actual bands to be used, we can speculate further (see pics in the blogs from Shaun and I below):
http://blog.wdwinfo.com/2013/04/06/disney-magicband-news-for-annual-passholders/
http://blog.wdwinfo.com/2013/05/17/first-look-disneys-mymagic-magicband
I'm excited to see everything when it's in stores! Don't plan on the accessories being available for everyone to purchase any time soon though. That won't happen until testing is complete and the bands are ready for public use.