Instructions
Load a saved game or begin a new game and play through until you reach the levels of Cortana, Floodgate and Halo if you're playing a single-player mission. Conversely, you can choose to play the multiplayer campaign, which allows you to select the level you wish to play through with up to three other friends. These are the only levels that feature the sword.
Locate a friendly Elite, the giant blue lizard warriors that are betraying their kind and engaging in a civil war during the game's storyline and wait for one to be killed. Search the ground near his carcass to find a sword. Conversely -- although somewhat underhanded -- cook a plasma grenade and place it on the back of an Elite. After it detonates, collect a sword (your ally will take no damage during the Mythic setting, though.)
Drain the energy shield of Arbiter, the Elite ally who is a controllable character during certain chapters of the game. This can be done by getting behind him when his shield is activated and shooting through his shield, which decreases its energy reserve. Once done, he surrenders his sword in an effort to recharge his shield, giving you the chance to pick it up from his feet. If you've already equipped the first sword you picked up, the second sword will automatically appear in your remaining hand.