[Radek]

(1) You need the Soul Trap spell. The "standard" soultrap it "touch" but you'd better create it yourself and make it "ranged", this will remove problems with casting a touch spell during a combat.
Once the spell is successfuly cast, you need to kill the creature before the spell wears off, keep this in mind when you select the duration of your spell.

(2) At any daedric ruins. The area with the ruins resets every time you enter it and contains (usually) 4 daedras. Therefore, check the daedras, enter the shrine, turn back, leave it (new 4 daedras will appear), repeat. It should not take it a long time before you get 2 Storm Atronachs.
Note: Golden Saints tend to cast Dispel Magic on themselves. If you haven't a soul trapping weapon or if you aren't enough fast then do not waste spell points on Golden Saints. Storm Atronachs cannot dispel the Soul Trap.