Here is the link: Spearhead. You must be logged into the GW site to get here. Here is the release info as well on what Spearhead is really is.
Spearhead is an official Expansion for Warhammer 40,000. It is a game of brutal tank battles and mechanised assaults, featuring armoured columns clashing across the wreckage-strewn plains of the 41st Millennium.
To play Spearhead all you need to do is download the PDF presented here. Once downloaded you'll find a file packed with all the information you need to get playing exciting tank battles, from rules and missions to 18 spearhead formations - including two spearheads taken from December 2010's White Dwarf and four new spearheads written especially for this update.
Thanks to Reds8n on warseer for being the first to notice this