Yen Press is publishing SAO, along with many other light novels, for the North American market. Please try and purchase official English localizations when possible. Links will be taken down as release dates for official copies are announced.
Volumes 11 through 15 are translated by Tap. You can visit his blog here.
Volume 11 – Alicization Turning – Amazon
Volume 12 – Alicization Running – Amazon
Volume 13 – Alicization Dividing – Amazon
Volume 14 – Alicization Uniting – Amazon
Volume 15 – Alicization Invading