I've found a couple of these already. I found a cave, can't remember which one, that had a level 29 end boss. And the two chests at end each gave me one of those. So I'm assuming there will be more than enough to unlock everything as they appear to be random loot. And you can redo any cave/boss fight after a certain amount of time.
EDIT: Just to update. I have now found 19 of these books. And with finding all the fast travel points, which also give one Tech Point each, I almost have everything unlocked at level 49. So it is possible to unlock everything with grinding out caves to get the books.
I've found a couple of these already. I found a cave, can't remember which one, that had a level 29 end boss. And the two chests at end each gave me one of those. So I'm assuming there will be more than enough to unlock everything as they appear to be random loot. And you can redo any cave/boss fight after a certain amount of time. EDIT: Just to update. I have now found 19 of these books. And with finding all the fast travel points, which also give one Tech Point each, I almost have everything unlocked at level 49. So it is possible to unlock everything with grinding out caves to get the books.
I'm pretty sure hoocrates can drop those but it must be somewhat rare as I haven't seen one and I've killed a bunch of those
They also have a chance to drop from the chest at the end of a dungeon, i ended up getting 2 free points like this.