Where do you find all the keys for the altair's armour in assassins creed 2?

Just look for the black Assassin symbol on your map in various towns which symblolise Assassin's Tombs where an Assassin seal can be found at the end of each mission in there. Once you have collected all 6 seals taek it back to the sanctuary in the Villa Auditore, Monteriggione and place them on the statues. Once this has been done a short cinematic will occur where you will have obtained the armour