Unlimited/easy Precursor Orbs:

Go to any oracle statue and trade metal head skull gems to start an orb search challenge. Go to the orb and wait for the clock to turn to 00:00. Even though it says 00:00, it takes another second for the time to run out (I.E. 00:00 is really 00:00.100) So wait one more second, and then press Square to dash at the orb as soon as time runs out and the mission failed screen comes up. You will get 3 orbs, and be able to retry.