Diagrams for "set" armor parts & weapons: Griffin School, Cat (Feline) School, Bear (Ursine) School or Wolf School are usually well hidden in chests, etc. deep inside dungeons or in a hard to reach areas so it is very hard to discover all of them by simply exploring the game world.
But some of the merchants found in the game sell special maps or notes which can help you. When you buy and read such map or note, it will start a "treasure hunt" quest so it's much easier to find the treasure becouse you can turn on map markers for such quest.
Any of the following notes starts the corresponding quest to find improvement diagrams (Parts 1 - 4) as well as the quest to find diagrams to make all the parts of the starting / basic feline gear.