I just clicked the little arrow next to Morning Musume in my iTunes party shuffle mode; I used to have this set up to go to the artist in my library, but I recently installed a new system, so instead it went to that artist on the iTunes Store. The crazy thing is that they actually have a ton of Morning Musume for sale on the USA version of the store! So of course I scrolled through the ordinarily pretty anemic J-Pop category to see what else they might have added; sure enough, there was clammbon!! At the moment they only have Musical for sale, but that's still pretty spectacular: clammbon music available outside of Japan for instant download, for only $10!
Update: Apparently the Canadian iTunes has even more clammbon music! Check your country's iTunes store!
