I think Aquapac have an on-line store but if not, you need the Whanganui model, that accommodates Kindle 3 and later (but not Kindle 2, that's a shade to big).
It's available on Amazon but only a market seller, see
here.
It's a great case, you can switch it on/off whilst in the bag, takes seconds to insert/remove and all the buttons etc are accessible. On my iPad version, the touchscreen works and sound is fine. I use it in the bath to watch TV
I reviewed the iPad version for my site last year, see
here.
It's lovely lying on a li-lo in the pool reading your favourite book and flicking cool water on to you every now and then