Oh the Places You'll Go!
Caverns of Frost - Fields of Slaughter
Icefall Caves - Fields of Slaughter
Fortified Buncker - The Arreat Gate
The Barracks - The Arreat Gate
Battlefield Stores - The Battlefields
The Foundry - The Battlefields
Cryder's Outpost - The Battlefields
The Forward Barracks - The Battlefields
The Underbridge - Rakkis Crossing
I was a bit more accurate with the books this time as I was tracking when I wrote this rather than doing it after I was nearly done with everything else.
Bloodstained Letter - The Keep (this is glitched for many people with it never dropping on certain characters, but should drop 100% off a Dead Soldier)
Ghom's Log - The Larder
Journal of Hansan Haile, Captain - Bastion's Keep Stronghold, near Vidar
Leah's Journal (13-16) - The Armory, below Leah
Morgan's Journal (1-3) - Morgan's Satchel, Skycrown Battlements/Stonefort
Battlefield Reports - UNKNOWN (The text suggests it would be around the battlefields/bridges)
Orders from Azmodan (1-6) - Messenger of Azmodan (Skycrown Battlements, Stonefort, The Keep, The Battlefields, Fields of Slaughter, Arreat Crater)
Historian of Arreat
Fall of the Barbarians (1-5) - Misplaced Packs, The Keep
The History of Bastion's Keep - Librarian's Scrolls (Can be found in The Keep and several other zones, usually right at the stairs at the start)
Revisiting this afterward it seems like we've found everything except the Battlefield Reports, which may be bugged like the Villager's Journal. No one's found a copy in weeks, so it's possible. The Bloodstained Letter seems to have glitched for many characters, and never drops despite not having the lore for it. Although it's short, the next act is finished up here (https://us.battle.net/d3/en/forum/topic/5151272462) and everything's already found and easy in it.