Don't do patrols. It will take forever if your goal is just one to upgrade. Do the mission Fist of Crota. Kill the sword guy and restart until I get it. I got one relatively fast then a second and third unexpectedly. But if your trying for one. It's your fastest encounter. It won't be a engram. It will pop up like u completed a section on the raid. And don't use Bounty xp to level. It requires u to kill hive so search YouTube on tips for a quick upgrade. Happy hunting.