I know the card appears in the raid section of the grimoire. The world item, however, is the sword carried by the swordbearer enemy type. That enemy type appears in the Fist of Crota story mission as well as in the Crota's End raid. That enemy type was much more plentiful before DLC 2, when Swordbearers would appear regularly during Earth and Moon patrols. The Ascendant Sword is what you pick up each time from them and it is the weapon they wield. Therefore, the advice I gave might work and I believe did work for me during The Dark Below.