Now I know that this mayb hard for most people to solo, so you may need a group.. but I almost always get at least 2 spellweave scrolls per lady mel run. Also a lot of the things in blighted grove drop them. They seem to be the higher level scrolls however, I am not sure the exact system in place but it seems that certain critters drop certain levels of scrolls. For example trogs tend to drop the lower scrolls, and I often have to go there to get thunderstorm. Lady Mel will give you the higher ones, word of death for sure, wildfire, etc. I tend to do things on fel side, I am superstitious about fel giving a higher drop rate and better loot.