Yeah, I know I got them off the troglodytes, Grobu, and Lurg, at leasts, as well as things like Swoop, dryads, changlings, and just about anything else in the ML dungeons. It MIGHT only be critters exclusive to the ML dungeons though, as everything I've listed is only found in ML, so it might not spawn the scrolls in critters found outside there (I assume because they'd need to have two different loot tables for them, based on location, and I don't think it works like that).
Good luck on getting them all though, as it didn't take me too long overall, although I don't actually have a spellweaver right now
And if you find yourself short a spell or two later and want the help, feel free to ask for them later