The blood dragon armour on Dragon Age: Origins can only be obtained by purchasing it from a specific vendor called, Bodhan Feddic, at your party camp, however tho you are already given one piece of the armour.
On the Otherhand if you mean the Blood Dragon Armour for Mass Effect then you need to activate the promo code before a specific date, as it is a Digital Download, that was downloaded long after the promotion, then you cannot have it i am afraid.
@XAlphazorX: The Blood Dragon Armor is only available from Bodhan Feddic in Dragon Age: Origins
IF you've entered the promotion code for it. If you haven't, then it's not available at any ingame merchant.