<spoiler>Obtainable on the lower part of Vengoth after giving 100 Vampire Lord Tokens to Storkus in the Vampire Hunter Quest. After Summer Update 2009 you can't get it there. But after 16 september 2009 CIP fixed that, so you can get a Blood Skull.
Additionally, after the patch on March 9th 2010, it is available in Vengoth Castle in a chest that was previously blocked. </spoiler>