MSDN Subscriptions just released windows 8 files on msdn subscriptions, you can get it with your subscription.

Windows 8 Client - https://msdn.microsoft.com/en-us/subscriptions/securedownloads/default.aspx?pv=36:449

Windows 8 Server - https://msdn.microsoft.com/en-us/subscriptions/securedownloads/default.aspx?pv=36:450

Thanks
RV