Excelsior

Where might I find beasties that drop the 8th circle spells amongst their loot?
Far and wide I have traversed the lands and deep ventured in to the traditional dungeons, yet I have not yet seen the pinacle spells of magery drop. I know that I could easily purchase a full spell book or find scribes to copy these spells for me but I would like to claim them for myself if possible. The "iron price" so to speak.
Might someone be able to offer me a pointer to such treasures can be found?

Find them off the higher caster Mobs. Doom Dungeon , Balrons maybe? Things of that nature. It might be a little easier just to have a player write them for your book though.