Equip a Shell with "wormspore extractor" and farm for engrams(wich will randomly give You wormspore when picking up engrams) in Court of Oryx. A bonus You get is the Crotas Bane reputation for each completion. Reciprocal rune: 25 rep Stolen rune: 50 rep Antiquated rune: 100 rep 3000 rep per package from Eris. You can also donate wormspore for reputation but it's like 1500 wormspore per package I think so it can take some time to grind. Sidenote: today Bungie increased the drop rate for artifacts from Eris packages.