Get it here:
Season Four is now available at most retailers. Here are the links:
Amazon US: http://www.amazon.com/dp/B00L3G007I/?tag=seasonfour-20
Amazon UK: http://www.amazon.co.uk/dp/B00L3G007I/?tag=seasonfour-21
Barnes & Noble: http://www.barnesandnoble.com/w/noble-intentions-lt-ryan/1119746552?ean=2940149805488
iDevice users – I recommend the Kindle app as Apple takes considerably longer to approve and publish books.