The new ones AirPort Extreme and AirPort Time Capsule equipped with the new Wi-Fi standard 802.11ac, were launched during WWDC 2013 and shortly after the presentation they were already available for purchase in the United States.
Here in Brazil, as we know, everything has to go through the National Telecommunications Agency. Because they have just been approved. Here is the Technical Compliance Certificate for the A1521 (AirPort Extreme) and A1470 (Time Capsule) models:
Below, the Regulatory Compliance Documents:
Now, the units sent for testing:
Although they are already listed on the Apple Online Store, Apple's new Wi-Fi bases are not yet available for sale, which is expected to change very soon. To learn a little more about the accessories including the poor differences between them, check the disassembly done by iFixit (AE, TC).