Amazon now has the Xbox One Stereo Headset Audio Adapter is available to order by clicking here:
http://www.amazon.com/Xbox-One-Stereo-Headset-Adapter/dp/B00IAVDOS6
These adapters sell out quick! Be sure to check the link above for the latest availability.
Helpful links: Xbox One Tracker and PS4 Tracker for the most recent inventory changes.