There's still a product page.

http://www.apple.com/shop/product/ME182LL/A/airport-time-cap...

I can imagine that they would want people to migrate to iCloud. That would be less helpful for those that don't have a (reliable) internet connection.

I have a great connection but I don't want my data in the cloud if I can avoid it.

I have it on good authority that Apple only sells adapters now.