Where can I find the Fire Atronachs that drop fire salts?

The smith in Riften requires 10 fire salts. I realize they are available from Fire Atronachs but where can I find these creatures? Also, do you recommend a level range for taking them on?

Here are some places where fire salt can be obtained:

• 1 can be stolen or purchased from Arcadia's Cauldron in Whiterun.
• 1 in Fort Amol Southwest from Windhelm .
• 3 may be available during the Hitting the Books quest.
• 1 can be found in Forsaken Cave on the right shelf next to the white phial
• 1 can be found during the The Black Star quest.
• 3 can be stolen from Septimus Signus in his outpost.
• 2 can be purchased from the Alchemist that appears when restoring the Thieves Guild.
• 2 can be found on the shelving to the left of the alchemy station after purchasing the alchemy lab decoration for Honeyside (Riften player housing).

Typically, whenever I find a dungeon that contains conjurers, there are some unbounded flame atronachs around.

On the south and east sides of Whiterun, there are several farms (Battle-Born and Chillfurrow).

Go south of there and you will come to a river: follow the river south and you will see a bridge on the left, crossing the river.

Cross the bridge and make a left (north) and there is a random encounter where a mage is fighting a flame atronach. By the time you get there the mage will be dead and you'll have to fight the flame atronach. You can get your fire salts that way.

This random encounter seems to reset itself at some point, so come back from time to time and you might find more wandering around.

(If you refer to this Skyrim map while using my directions and you'll find it no problem.)