The first radio CD of the now ended (last episode on 2011-05-07) Natural Radio from http://hibiki/radio.jp/ They now have WEIBS, but I don't think it has the chemistry of the original radio show.
Contains episode 1 (2010-09-11) to episode 12 (2010-11-27), plus one newly recorded episode in 128kbps MP3 format.
Ani-mon store does not ship overseas, so I had to have a friend in Japan buy this and bring it over when he was visiting. So, I have no idea what I'm going to do when the next volume comes out.