There's still two months to go and the Dota 2 International Compendium sales are already past the 10 million mark and closing in on last years record 10.9 million. At the rate sales are going, the stretch goal of 15 million set by Steam is well within the realm of possibility. 

To purchase your Compendium and check out the different tiers of rewards, head to the the offical Dota 2 Compendium page.