Barbican Hamlet website. Remember that although they are sold out, some tickets will become available, so keep an eye on that site and their FB page.
They sold out on 11-August-2014, going by their FB.
But the £10 tickets will still be available in 2015. That's 100 tickets for each performance, including a surcharge, per their official box office site.
Cumberbatch's Hamlet most in-demand show of all time at the Telegraph. Plus Benedict Cumberbatch: a Hamlet worth waiting for.