What is the quickest way to get Void Salts in Skyrim?

The other day I got the Nightingale armour and I have a pretty high smithing skill but I need Void Salts to upgrade the nightingale armour. Any suggestions?
I've tried looking at alchemy shops, my houses (Proudspire Manor, Hjerim and Honeyside), but none are there.

There is an overview on fandom.com of places where you can find Void Salts:

• Looted from Storm Atronachs.
• Can be very rarely looted from Falmer.
• Can be bought from alchemist's shops.
• Proudspire Manor alchemy lab in Solitude.
• Honeyside alchemy lab in Riften.
• Hjerim alchemy lab in Windhelm.
• Arch-Mage's Quarters in the College of Winterhold.
• Arcadia's Cauldron in Whiterun, on a shelf.
• Fletcher in Solitude, on a shelf.
• May be found in apothecary's satchels.
• May be awarded by Narfi at the end of his quest "The Straw that Broke."
• Can be obtained at Sky Haven Temple.
• Can be stolen in Calixto's House of Curiosities in Windhelm.
• In Sadri's Used Wares in Windhelm, on the shelves. He also sells this sample.
• 1 can be found in Valerica's Study in Castle Volkihar.
• On a shelf inside of Ragnvald Temple.

Note that this was the first hit when googling for 'Void Salts' - that was the 'quickest way' to get them. In-game, it depends on your character, and is therefore hard to answer.