He got the guns in another state im assuming arizona. He wrote in his mainfesto how easy it was for him to purchase silencers especially since he wasnt from the state they were purchased in.
Wait, what was I thinking? It'd be illegal for a CA resident like him to purchase those guns out of state (legally). In the world of guns, most people recognize California as having the strictest laws and any California resident wouldn't be touched with a ten foot pole in any Arizona gun store trying to buy CA-restricted items. The fact that a .50 cal BMG rifle is illegal here would make it illegal for a dealer of any state to sell him one.
I doubt it was that easy to purchase supressors especially out of state, as it would again be illegal for a CA resident to purchase one, even in AZ. Silencers are regulated by the National Firearms Act which means much more red tape. Much more than the .50 cals. They're a 'Class III' 'weapon.'
Owning one involves living in a place that they're legal. After that you need to find a Class III dealer. Then you need to pay for the the 'weapon' (silencer) and have the BATFE approve transfer of it to the dealer. Weeks later after that's approved, you need to fill out another form with serial numbers as well as your photo, fingerprints (unless you use an NFA Trust or corporation/LLC which means more money and more time spent), a $200 check, and the signature of a chief law enforcement officer (unless you use a trust/corp./LLC). You'll also need a certificate of compliance completed. After those forms are accepted and approved weeks later, THEN the dealer can release the 'weapon' to you. That's for each NFA restricted item, baby.
All of the above is assuming you live in a state that allows silencer ownership. CA does not. And there is no way an AZ dealer would/could go through that all for a CA resident. They'd laugh you out the door. The forms would have zero chance of getting approved anyway. What I'm getting at is that if he got them legally, he couldn't be a California resident, and if he got them easily, he got them illegally.