kneecapper, fallout 4

Anyone know how to obtain a kneecapper weapon pon fallout 4. legendary enemies drop them but i think its only enemies in certain areas, can someone point me in the right direction of what areas and which legendarys drop them, thanks in advance. Im playing the ps4 version. thanks
Answer #1

* It is possible to obtain two Kneecappers. The first by pickpocketing it from Ronald Laren while he is in Girdershade. The second by collecting another from his corpse if he is sent to the Nuka-Cola plant using dialog from the Black Widow perk.
* If Ronald learns of Sierra's death, he will refer to the Kneecapper by name as he attacks the Lone Wanderer.
Answer #2
That’s fallout 3 mate, not fallout 4