For those who, like me, simply must have all quests completed before the game's finale. This is a map checklist for where to find the required items. Some items are hidden in remote parts of maps and/or behind perception checks. This list is composed in 1.2.1 - 1.3 era. I was making this checklist for my own use, and therefore didn't bother with the screeenshots. Sorry about that. At least you'd know where to look if you missed something. Unless you've already advanced to the next chapter, then you'd know how many items you missed.
Update: I also added a list of locations for the Elven Notes the Storyteller needs for his quest.
Update2: Included the crafting components from the Dance of Masks DLC.

The Storyteller can craft an item from a core component and crafting materials. The crafting materials include: Magic Essense, Cold Iron, Demon Blood and Hide of a Magical Creature.

The Covenant of the Inheritor: Piece of a Holy Symbol + 5 ME
Ring of Summoning: Melted Shard of a Ring + 4 ME + 2 CI
The Stern Hand: Shard of Knight's Bracers + 1 ME + 4 CI + 2 DB
Ronneck's Sacrifice: Rune-covered Ancient Leather Scrap + 3 ME + 1 CI + 2 DB + 2 HMC
The Bound of Possibility: Ancient Scrap of Script-Covered Leather + 5 ME + 2 CI + 2 DB + 3 HMC
(there's an achievement for crafting it)
Shy Lily's Helmet: Crumpled Demon Helmet + 2 ME + 3 CI + 4 DB + 1 HMC

Therefore, in total you need:
Magic Essense: 20
Cold Iron: 12
Demon Blood: 10
Hide of a Magical Creature: 6

Piece of a Holy Symbol - Kenabres Market Square (ch1)
Melted Shard of a Ring - Houndheart Campsite (ch2)
Shard of Knight's Bracers - Assault on Drezen (ch2)
Rune-covered Ancient Leather Scrap - Wintersun (ch3)
Ancient Scrap of Script-Covered Leather - Areelu's Laboratory (ch3)
Crumpled Demon Helmet - Upper City (ch4)

Estrod Tower (ch1)
Blackwing Library (ch1)
Gwerm's Mansion (ch1)
Grey Garrison (ch1)
Grey Garrison (ch1)
Grey Garrison (ch1)
Nightingale Grove (ch2)
Underground Hideout (ch2)
Reliable Redoubt (ch2)
Assault on Drezen (ch2)
Assault on Drezen (ch2)
Ashen Grotto (ch3)
Temple of the Good Hunt (ch3)
Molten Scar (ch3)
Shrine of Sacrilege (ch3)
Areelu's Laboratory (ch3)
Midnight Fane (ch3)
Lower City (ch4)
Nexus, hidden part (ch4)
Return to Drezen, tavern (ch5)
Bladesmith Workshop (ch5)
Dance of Masks DLC, Razmir's Palace, loot the laboratory in the book episode (ch5)

Total count: 21 + 1 (DLC)

Moondance Meadow (ch2)
Lost Chapel (ch2)
Assault on Drezen (ch2)
Greengates (ch3)
Ravaged Long House (ch3)
Ivory Sanctum (ch3)
Areelu's Laboratory (ch3)
Lower City, tavern (ch4)
Middle City, Hidden Abode (ch4)
Upper City (ch4)
Return to Drezen (ch5)
Return to Drezen (ch5)
Dance of Masks DLC, Razmir's Palace, loot the laboratory in the book episode (ch5)

Total count: 12 + 1 (DLC)

Shrine of Sacrilege (ch3)
Artisan's Tower (ch3)
Hellknights Outpost (ch3)
Legacy of the Ancients (ch3)
Ivory Sanctum (ch3)
Ivory Sanctum (ch3)
Nexus (ch4)
Lower City (ch4)
Upper City, inside a house (ch4)
Jubilost Encounter (ch5)
Dance of Masks DLC, Razmir's Palace, loot the laboratory in the book episode (ch5)

Total count: 10 + 1 (DLC)

Nexus (ch4)
Middle City (ch4)
Upper City (ch4)
Upper City, inside a house (ch4)
Return to Drezen, prison (ch5)
Return to Drezen, citadel (ch5)
Jubilost Encounter (ch5)
Dance of Masks DLC, Razmir's Palace, loot the laboratory in the book episode (ch5)

Total count: 7 + 1 (DLC)

Gray Garrison (ch1) - this one is unique and is used to complete the Storyteller's first quest
Conundrum Unsolved (ch2) - requires solving a puzzle
Inconspicuous Camp (ch2)
Temple of the Good Hunt (ch3)
Areelu's Laboratory (ch3)
Areelu's Laboratory (ch3)
Artisan's Tower (ch3) - must kill Devarra the Woundwyrm before she burns it
Ivory Sanctum (ch3)
Sacred Lands (ch3)
Molten Scar (ch3) - this one is unique and requires decryption, which might be hard due to bloodstains if the vrock holding it is killed
Core of the Riddle (ch3) - requires solving a puzzle
Nexus (ch4)
Mage's Tower (ch4)
Forgotten Secrets (ch5) - requires solving a puzzle
Legacy of the Ancients (ch5) - requires solving a puzzle
Final Veil (ch5) - requires solving a puzzle
Heart of Mystery (ch5) - requires solving a puzzle
Enigma (ch5)
Iz (ch5)
Threshold (ch6) - the first level. Must return to the Storyteller right after acquiring the note, and not proceed to the second floor

There are 20 Elven Notes in total throughout the game. The Storyteller needs 19 notes to remember his own story and complete his quest. The Storyteller remembers a part of his past for the first note, then another one for each third note brought to him - a total of 7 parts. The final 20th note reveals a story about Areelu's past and provides for an easier reading through the combined Lexicon of Paradox (1st and 2nd halves put together), unlocking one of the prerequisites for the Ascension Ending.

Did I miss something? I could've. Please, let me know.