The new set runes can be obtained in 3 ways:
- Whenever you polish a precious runestone there is a small chance that it will turn into a set rune. From what I've heard, the chance is at most 1%. A set rune rolled like this is random so even if you get "lucky", it might not have been what you were looking for. Set runes cannot be re-polished, but they can be dissolved and if I remember correctly, you get a Gaia stone back.
- If you spend 6k gems in one day for re-polishing runes, you get a chest as a reward (or consolation prize). The set rune in the chest changes each day, but it is known ahead which rune it will be. So my suggestion is: wait with re-polishing runestones until the chest contains a set rune that you want.
- Purchase it, duh, it's Lilith after all.