Dude, just run around Archer's Line. I racked up over 70+ in less than 20 mins. If you see there are other guardians there, just leave the area and go to another area like Hellmouth or Anchor of Light then come back to it 30 seconds later. Or, you can join those guardians by either pointing or dance at the helium or chest, they will do the same once they realize you are helping them.