The new releases of Windows OS products (both Windows 8.1 and Windows Server 2012 R2) are actually in a RTM state for OEM and will be public available on October (probably the 17th or the 18th). Actually, in the last days, Microsoft has announced that the RTM is also available on MSDN and Technet. Or you can simple ask to download the evaluation product (but in this case it’s just a beta version).