Here are skills that can stun... (please add if i missed something) XD
stun from BL:
death blow - martialist
minotaur stomp - martialist
anger's explosion - crimsonate
concussive rend - crimsonate
concussion - redhand
stun from Gadgeteer:
refine special electron canon 1 step - marksman
stunning refire - marksman
suppresive fire - marksman
you can also have stun from a weapon (hammer or other) as long as it has a stun rate..
you can also stun with active skills but if you want to stunlock while attacking then you can rely on the passive skills (refer to in game skill descriptions)
and i think rend flesh effect is bleeding...