This is a partial list of the loot from PS bosses that cannot be sold. It is not all-encompassing but.. eh. Close enough. Whether you want to put all, most, some or only a few of these items in the NPCs is your call.

-Demon Legs
Skullcrusher
-Demon Helmet
-Arbalest
-Backpack of Holding
Hellforged Axe
Obsidian Truncheon
Divine Plate (Should sell to Rashid but doesn't.)
The Stomper
Demonwing Axe
Fireborn Giant Armor
Earthborn Titan Armor
Oceanborn Leviathan Armor
Ravenwing
Titan Axe
Frozen Plate
Robe of the Ice Queen
Spellbook of Lost Souls
Spellbook of Mind Control
Spellbook of Warding
Spellbook of Dark Mysteries
Spellscroll of Prophecies
Avenger
Master Archer's Armor
Emerald Sword
Bows (Devil's Chain Bolter, etc)
Devileye
Dragon Scale Helmet
Dragon Scale Boots
Havoc Blade
Runed Sword
Star Tear
Nidalees Spear
The Epiphany
Arcane Staff
Mythril Axe
Bronze Trophy
Demonbone

    The Djinn [Loot] Item Dealer NPC should have the following items, based on the inventory of the four different Djinns on RL Tibia: (Prices taken from wiki, no guarantees that there aren't post-8.6 items.)

    Ancient Shield          900
    Angelic Axe     5,000
    Ankh    100
    Axe Ring        100
    Black Shield            800
    Boots of Haste  30,000
    Bronze Amulet   50
    Butcher's Axe   18,000
    Club Ring       100
    Dark Armor              400
    Dark Helmet             250
    Dragon Necklace         100
    Dragon Shield   4,000
    Dwarven Ring    100
    Earth Knight Axe          2000
    Elven Amulet    100
    Energy Knight Axe         2000
    Energy Ring     100
    Earth Spike Sword       1,000
    Earth War Hammer        1,200
    Energy Spike Sword      1,000
    Energy War Hammer       1,200
    Fiery Knight Axe          2000
    Fiery Spike Sword       1,000
    Fiery War Hammer        1,200
    Garlic Necklace         50
    Glorious Axe    3,000
    Hailstorm Rod   3,000
    Icy Knight Axe          2000
    Icy Spike Sword         1,000
    Icy War Hammer  1,200
    Life Crystal    50
    Life Ring       50
    Magic Light Wand        35
    Might Ring      250
    Mind Stone      100
    Moonlight Rod   200
    Mysterious Fetish       50
    Necrotic Rod    1,000
    Noble Armor     900
    Northwind Rod   1,500
    Obsidian Lance  500
    Orb     750
    Ornamented Axe          20000
    Phoenix Shield  16,000
    Poison Dagger   50
    Power Ring      50
    Protection Amulet       100
    Queen's Sceptre         20,000
    Ring of Healing         100
    Scimitar                150
    Silver Amulet   50
    Snakebite Rod   100
    Springsprout Rod        3,600
    Strange Talisman        30
    Stealth Ring    200
    Stone Skin Amulet       500
    Strange Helmet          500
    Sword Ring      100
    Terra Rod       2,000
    Thaian Sword    16,000
    Time Ring       100
    Titan Axe               4000
    Underworld Rod  4,400
    Wand of Cosmic Energy   2,000
    Wand of Decay   1,000
    Wand of Draconia        1,500
    Wand of Dragonbreath    200
    Wand of Inferno         3,000
    Wand of Starstorm       3,600
    Wand of Voodoo  4,400
    Wand of Vortex  100


    The following items are missing from the Djinn NPC:
    Bandana         150
    Beetle Necklace         1,500
    Blacksteel Sword        6,000
    Blessed Sceptre         40,000
    Chain Bolter    40,000
    Cobra Crown     50,000
    Coconut Shoes   500
    Composite Hornbow       25,000
    Crystal Mace    12,000
    Crystal Ring    250
    Crystalline Armor       16,000
    Divine Plate    55,000
    Djinn Blade     15,000
    Dreaded Cleaver         10,000
    Earth War Axe   12,000
    Elvish Bow      2,000
    Energy War Axe  12,000
    Fiery War Axe   12,000
    Flower Dress    1,000
    Flower Wreath   500
    Heavy Trident   2,000
    Icy War Axe     12,000
    Lavos Armor     16,000
    Leviathan's Amulet      3,000
    Magic Plate Armor       90,000
    Mastermind Shield       50,000
    Orcish Maul     6,000
    Patched Boots   2,000
    Pharaoh Sword   23,000
    Sacred Tree Amulet      3,000
    Shockwave Amulet        3,000
    Swamplair Armor         16,000
    Tempest Shield  35,000
    The Justice Seeker      40,000
    War Horn        8,000
    Witch Hat       5,000