One set can be found in a wardrobe in Dark Squall's headquarters under the Black Knight Fortress during the While Guthix Sleeps quest. Also obtained as a random drop from elite black knights all over the dungeon.
Nice looking leg armour with good defence. Required for completing While Guthix Sleeps. Can be stored in an Armour Case in the Costume Room of a member's Player-Owned House.
Notes:
Can not be smithed. Require at least 40 Defence to wear.