Benen, im wondering if your browser is defaulting to thermarest's Australian site (if such a thing exists?). I've noticed this a lot when traveling internationally. For instance, I've tried to visit American sites such as Google.com or cnn.com and it'll take me to an interface that is specific to the country that I'm logging on from.
When I click Ken's link above, I can see under the big "Neoair" heading, a specs tab that shows all the different sizes that they've always offered. Moreover, when you scroll down to the bottom of the page, there's a drop down menu that lets you search for all the sizes, and which online retailers carry them. Rest assured, all the sizes are still available. Something funny is going on with the browser it seems.