Agility orbs (green tiered orbs) are the easiest way to get this. They are usually on buildings small and high, the higher the area the more powerful the orb is (more value). Some agility orbs will require a higher agility level (higher jumping power). All will make a sound when are are pretty close to it and you should see a short beam of green light about them. Seeing as there is 750 agility orbs in the game then collecting 100 shouldn't be too hard in between objectives.