You get the different bits from different spawn. Most find the common pieces from say the swoops or misama's.

The rarer pieces drop from the boss creatures.

I have copied this chart i have if it helps


Dread Horn

* Elven Leafweave
* Legs
* Death's Essence
* Tunic
* Marksman's Set
* Feathernock (quiver)
* Assassin Armor
* Leggings

Irk

* Plate of Honor
* Gloves

Lady Jennifyr

* Assassin armor ?
* Tunic ?

Lady Lissith

* Greymist Armor
* Tunic
* Plate of Honor
* Sleeves
* Gorget
* Death's Essence
* Gloves

Lady Melisande

* Assassin Armor
* Leggings
* Death's Essence
* Leggings
* Greymist Armor
* Sleeves
* Juggernaut Set
* Evocaricus Sword
* Maleki's Honor Shield
* Marksman's Set
* Feathernock (quiver)
* Swiftflight (bow)
* Plate of Honor
* Leggings

Lady Sabrix

* Hunters Garb
* Legs
* Gloves
* Plate of Honor
* Sleeves

Lurg

* Myrmidon Armor
* Gorget
* Gloves
* Assassin Armour
* Sleeves

Miasma

* Plate of Honor
* Arms
* Gorget
* Myrmidon Armor
* Gorget
* Gloves
* Sleeves
* Leggings
* Elven Leafweave
* Leggings
* Death's Essence
* Tunic
* Gloves
* Legs
* Greymist Armor
* Gloves
* Sleeves
* Assassin Armor
* Tunic
* Sleeves
* Hunters Garb
* Gloves
* Leggings

Monstrous Interred Grizzle

* Juggernaut Set
* Maleki's Honor Shield
* Plate of Honor
* Gorget
* Greymist Armor
* Tunic

Shimmering Effusion

* Juggernaut Set
* Maleki's Honor Shield
* Marksmen
* Swiftlight + feathernock
* Hunters Garb
* Gloves

Swoop

* Assassin Armour
* Tunic
* Sleeves
* Death's Essance
* Tunic
* Myrmidon Armor
* Gloves
* Sleeves
* Legs
* Gorgot
* Elven Leafweave
* Gloves
* Legs
* Sleeves
* Plate of Honor
* Gloves
* Gorgot
* Arms
* Hunters Garb
* Legs
* Gloves
* Sleeves
* Tunic
* Greymist Armor
* Gloves
* Arms

Travesty

* Juggernaut Set
* Maleki's Honor Shield
* Assassin Armor
* Sleeves
* Leggings
* Gloves
* Plate of Honor
* Gloves
* Tunic
* Sleeves

Virulent

* Juggernaut Set
* Maleki's Honor Shield
* Hunters Garb
* Leggings


Common & Rare Pieces
Set Name Common Pieces / Rare Pieces
Hunter's Armor legs, gloves / tunic, gorget
Death's Essence tunic, legs, gloves / helmet, arms
Assassin tunic, arms / gloves, legs
Greymist arms, gloves / tunic, legs
Myrmidon legs, gloves, arms / gorget, tunic, bascinet
Honor Plate arms, gloves, gorget / tunic, legs, helm