The rest I have not made a note of, but this is a good place to post findings and requests so as not to spoil for other Skull hunters.

The only one I can not get is Ulfric's. He is already dead. I have about four pages of notes already for locations that I will post in the next day or so for anyone who is interested in them. Also, if there is a character in your game that is already dead, I know how to bring them back not using the resurrect cheat code. There is another one. It does not work on Ulfric however. Everything in his inventory is gone but his axe. If anyone is needing to know what to do, ask and I will tell you. It works to bring any character back into the game once gone.

Riften:
Brynjolf- Bluestorm Skull
Mercer- Rune Frost Skull
Garthar- Violetstorm Skull
Etienne Rarnis- Snowfur HUnter Skull
Cynric Endell- Grayman Skull
Rune- Painted Skull
Ravyn Imyan- Lichen Skull
Sapphire- Fox Pelt Skull
Vipir the Fleet- Yellow Doom Skull
Delvin Mallory- Penitus Grey Skull
Vekel the Man- Whiterun Skull
Vex- Windhelm Shield Skull
Dirge- Ravenmain Skull
Vanryth Gatharian- Whiterun Shield Skull
Hafjorg- Whitestorm Skull
Elgrim- Argonian Skin Hunter Skull
Brand-Shei- Vangeful Skull
Haelga- White Rock Skull
Talen-Jei- Scale Skull
Dinya Balu- Robo Gray Skull
Sigaar- Gowned Skull
Hofgrir Horse-Crusher- Bear Skull
Romlyn Dreth- Mourners Skull

Draven Llanith- Redguard Skull
Synda Llanith- Veridian Skull
M'aiq The Liar- Forest Dragon Skull
Karliah- Dawnstar Skull

Filnjar- Vampire Eye Skull

Gemma Uriel- White Horse Hunter Skull

Windhelm:
Dalan Merchad- Mothman Skull
Rolff Stone Fist- Moss Skull
Viola Giordano- Yellow Skull
Torbjorn Shatter Shield- Toxic Skull
Torsten Cruel Sea- Twain Doom Skull
Nils- Green Stone Skull
Jarl Skald- Strassus Skull
Thaena- Solitude Skull
Captain Lonely Gale- Deer Hunter Skull
Jorleif- Dawnstar Shield Skull
Sifnar Ironkettle- Rising Doom Skull
Jarl Korir- Falkreath Shield Skull
Calixto Corrium- Charred Skull
Hermir Strong-Heart- Argonia Skull
Niranye- Hrothgar Skull
Revyn Sadri- Marune Dragon Skull
Alfarenn- Gowned Skull
Ra' zhinda- Markarth Shield Skull

Whiterun:
Bjorlam- Gowned Skull
Sigurd- Leaf Skull
Belethor- Sovenguard Skull
Heimskr- Afterman Skull
Fralia Gray-Mane- Temple Skull
Nazeem- Grass Skull
Jon Battle-Born- Crystal Skull
Saadia- Priestess Skull
Uthgerd the Unbroken- White Rage Skull
Olfrid Battle-Born- Ice Skull
Ysolda- Winterhold Shield Skull
Brill- Affronted Skull
Olfina Gray-Mane- Hjaalmarch Shield Skull
Kodlak Whitemane- Emparor Skull
Torvar- Vampiric Skull
Najada Stonearm- Hjaalmarch Skull
Ria- Moss Skull
Vilkas- Winterhold Skull
Farkas- Snowcat Hunter Skull
Skjor- Rough Emerald Skull
Danica Pure-Spring- Packers Skull
Andurs- Gravel Skull
Amren- Castle Skull
Fianna- Summerset Skull

Dark Brotherhood:
Astrid- Groom Skull
Sabjorn- Black Beach Skull
Nazir- Green Rock Skull
Cicero- Graymain Skull

It may be a while till I find more and type them up. I am waiting for the next mod to come out till I get any further in the game. Since I am almost done with it, and I have way to much done to want to restart, again, I will start adding more cities/people in a while. Feel free, anyone, to add to what I have started.

On a side note, the thieves guild people, are a bit harder to pickpocket. Namely, Vex, Delvin, and Brynjolf. Mercer was already dead on my game, but like I said, I know a way to spawn them back and then just re-kill them after you get the skull. Happy hunting! :)

you have to kill or pickpocket to get them? Oh noooo