Overview
These are some of the places, where you can find Grand Soul Gems. Assuming you’re doing the “Vampire Cure” quest line, I’m gonna start with the easiest and most accessible ones.
Static locations
- Arcane University – 1 empty gem along with two filled gems in a display case in the lobby
- Chorrol Mages Guild – 2 empty gems, first one in a display case behind the stairs, second one in the next room, also in a display case along with two filled gems
- Drakelowe, witches’ hut – 1 empty gem in a bowl in the bassement (accessed through trapdoor in the fireplace)
Vendors
- Mages Guild sellers – Each guild has at least one for sale (can be pickpocketed)
- Imperial City Market District, Mistic Emporium – Calindil (can be pickpocketed)
Dungeons
- Three gems are added to previously non-existing areas in dungeons nearby Drakelowe (triggered by the questline “Vampire Cure”)
- Crayfish Cave, Nornal, Squandered Mine – Behind hidden rock walls/doors
- Any dungeon, after achieving level 11 – 5% chance of appearence
Feel free to comment about any other locations you know of.
Sources: [link], TES Wiki [elderscrolls.wikia.com], Gamefaqs [www.gamefaqs.com], my own head.