Certain scroll simply doesnt have alot of mobs that are easily or often farmed making them extremly rare. Adding them to more mobs to make them more readily available, or adding a way to exchange for them. This could be with pq points/ spirit points etc. The scroll i presonally have an issue finding is the Dark scroll for dagger 30%, every day for about 7-8 days ive checked market for them, not one has been for sale. Could be many more scrolls with this issue but this is the one i have.