Ive taken this list from a forum online, so not my own work, but this'll save people the faff of having to alt tab like I did! Below are the locations and the effects of the battle accessories in the game. Again, I cant take credit for this list, it was found on the PS Trophy forums and compiled by user Zertonium! :)

Battle Accessories that randomly drop from defeated enemy Officers from Battle Stages:

Amaterasu's Sphere - Health
Himiko's Charm - Fortitude
Tengu Sandals - Alacrity
Demon Crook - Equestrian
Spirit Fox Tail - Musou +
Military Treatise - Spirit +
Beckoning Cat - Fortune
Daybreak Armor - Stability
Ancient Mirror - Bravery
Hannya Mask - Determination
White Rabbit Leggings - Resolve
Earth Gauntlet - Economy
Ninja Attire - Euphoria
Secrets of Courage - Wisdom


Battle Accessories dropped by a "Secret Treasure Bearer" that has a random chance of spawning in each Exploration Map: (If you already have the Battle Accessory from the "Bearer" of the Exploration Map, you will get a Conch Shell instead.)

Hakusan Amulet - Eagle Eye - Sanada Homeland
Orochi Gauntlet - Acquisition - Mt. Asama Foothills
Snakeskin Drum - Nullification - Lake Suwa Banks
Saddle of Rebirth - Resurrection - Kiso Road
Demon's Mallet - Wealth - Mt. Kokuzo
Dragonwood Flute - Mastery - Hokkoku Road
Heavenly Brace - Health, Rampage - Yamazaki
Kojoro's Teardrop - Fortitude, Impulse - Iga Mountains
Golden Lion Armor - Alacrity, Equestrian, Awakening - Mt. Shigi
Conqueror's Saddle - Equestrian, Musou +, Paladin - Komoro
Demonspawn Mask - Alacrity, Musou +, Spirit +, Cavalier - Kimi Pass
Ancient Scroll - Health, Fortitude, Spirit +, Constitution - Kii Mountains


Definitions of each passive effect:

Acquisition - Acquire high-quality battlefield items more easily.
Alacrity - Increase your movement speed.
Awakening - Gradually fill the Musou Gauge while the Spirit Gauge is full.
Bravery - Decrease damage taken from enemy officers.
Cavalier - Gradually fill the Musou Gauge while mounted.
Constitution - Increase the amount the Health Gauge refills by.
Determination - Increase Attack strength and Defense when Health is very low.
Eagle Eye - Occasionally obtain more materials.
Economy - There is a chance your Spirit Gauge will not decrease when performing a Spirit Charge.
Equestrian - Increase Attack strength and Defense when mounted.
Euphoria - There is a chance your movement speed will increase after you defeat an officer.
Fortitude - Decrease damage taken from enemy attacks.
Fortune - Fortunate occurrences will increase.
Health - Increase your Health.
Impulse - Gradually fill the Musou Gauge while moving.
Mastery - Increase weapon Proficiency more easily.
Musou + -Increase the amount by which the Musou Gauge fills.
Nullification - Decrease damage taken from enemies' elemental attacks.
Paladin - Gradually fill the Spirit Gauge while mounted.
Rampage - Gradually fill the Spirit Gauge while moving.
Resolve - Gradually fill the Spirit Gauge when Health is very low.
Resurrection - When defeated, recover one time with limited amount of Health.
Spirit + - Increase the amount by which the Spirit Gauge fills.
Stability - Maintain balance when hit by an enemy attack.
Wealth - Increase the chances of receiving Gold when defeating enemies.
Wisdom - Earn additional EXP when defeating enemies.