The webpages definitively went up a couple of days ago. I posted the links on saterday IIRC.
e.g. for Greninja:
http://www.amazon.de/dp/B00VK5P27U/
I don't know whether there has been stock, though. It was already "out of stock" when I found the pages. Could have always been this way. But last time Amazon.de created Amiibo pages (for the first 6 Amiibos of Wave 4), stock was added just a couple hours after the page (page during the night, stock in the afternoon). It's strange if they created the webpages ~3-4 days ago and still haven't open preorders.
Pages for other announced Amiibos have *not* been created yet. And pages for Wave 4b Amiibos on Amazon.fr were only created today, when stock arrived (got a "404" this morning, or rather a redirection in fact), and same on UK (still a redirection, last time I checked)