Apparently, Shimano are famous for promoting their new stuff way before it's available in 'normal' (large) quantities. I dunno why.
The guy at my shop said it was the same when 10sp first came out. Maybe they think it generates more 'desire' and interest if it's hard to get.

I've made inquiries about the new C50 carbon/alu clincher wheelset, and it's the same story. One of our local online sellers says they won't be available 'til November, even though they were promoted in magazines as a new product many, many months ago