There are several ways to obtain a fragment or a full scroll.
The following mobs have a chance to drop a fragment:
Auroran Guardian Vyrava
Diamond Shores Razorbeak
Diamond Shores Crab
Diamond Shores Turtle
Diamond Shores Draugorc
Nuimari Stag
Nuimari Doe
Heedmar Buffalo
Gnoll Wanderer
Giant Pilgrim
Heedmar Owl
Returning Greenman
Calmlands Skyfin
Calmlands Boar
Marcala Ant
Marcala Giant Scorpion
100% drop rate of a fragment:
Harbinger (boss)
Sea Spirit General (boss)
Aragog, Spinning Darkness (boss)
Has a small chance to drop the scroll:
Ascension Crate (can be found in Improved Guild Shop)