's Concussive Blows: Braum's basic attacks and Winter's Bite each apply Concussive Blows to his target for 4 seconds, stacking up to 4 times. Once the first stack has been applied, any allied champion's basic attack on the target generates an additional stack.
- Upon reaching 4 stacks, the target is Stun icon stunned for 1.25 / 1.5 / 1.75 seconds and takes 40 - 176 (based on level) magic damage.
's Shield of Daybreak: Leona's next basic attack gains range, deals bonus magic damage to her target and Stun icon stuns them for 1.25 seconds.
's Bear Stance: Active: For a few seconds, Udyr gains bonus movement speed, ignores unit collision, and dashes towards nearby enemy champions upon Stun icon stunning them with a basic attack.
- Stance: Udyr's basic attacks Stun icon stun his target for 1 second. This effect cannot occur on the same target more than once every few seconds.
I think that's everyone with a Stun on a basic attack. Thought each is part of an ability tied to it. You will have to check ALL of the champions with stuns. I think I got all the ones with Stuns on abilities tied to auto attacks though besides
which you mentioned already. Check here