Ebay - that's were you go to find a Wraith Lord sword, only it'll need to be cut down to look right. Many folks who substitute it for the Dawn Blade, then is just looks Farsight robbed some Eldar for the sword.
EDIT: Edited to add "Dawn Blade with Ork Gubbins""Itz a 'Relic Weapon'. Soze wot eva youse doo, don't be puttin' da Ork Gubbins on "Da Dawn Choppa!" - Big Mek Gogs