While I haven't found everything, or even finished my first playthrough yet, I have found parts of each set:
Dragon Wizard:

Dragon Wizard Cuirass: was given after mind reading the tree that likes to zap people

Dragon Wizard Bracers: are in a chest in the far corner of the room where you pick the "flower that does not exist", in the temple of nimir as mind reading the ghost reveals there is a button behind the first chest.

Dragon Wizard helmet: is found in Gula's Chest, after curing him of his unfortunate curse.

Dragon Wizard leggings: are found in the chest in Laeniel's Room in Hansel's house.

Dragon Wizard earrings: magically appeared in inventory after mindreading Ursula the witch, who thinks about enchanted earrings. (I let her go)


Shadow Archer:

Shadow Archer Cuirass: is found if you side with willy against the assassins, and kill them.

Shadow Archer bracelet: was found in the jewelery box in the room where Abbott was trapped in, inside the forgotten crypt.

Shadow Archer: pants were in a chest in a small treasure room in the temple of nimir

Shadow Archer: gloves were in a chest in the healer house, after mind reading the guy lying by the door in the bed.


Viper:

Viper Cuirass: is given when mindreading the guy that rewards you for killing targets on the wanted poster, and asking about it.

Viper Belt: is looted off of General Luxurious

Viper Leggings: are found in a chest in the back of the locked room in the sewer tunnels in crow's nest. Mind reading the chef there reveals there are buttons next to the lower torches as you cross the bridge-path to his room.

Viper gloves: are found in a chest in the secret room in the basement of the haunted playhouse, opened by the button next to the desk

Viper helm: appears in a jewel box that materializes after arranging the paintings in the top room of the Phoenix Inn in the right order, 1st painting move up once, 2nd do not move, 3rd painting move up 3 times.