Every state has a mental health agency that provides free or nearly free psychiatric services regardless of one's ability to pay. They are basically pill mills that dispense one or more of the psychiatric drugs that have been shown to be disproportionately associated with acts of violence.It means that we have a society where not everyone can afford to address mental health issues.
One can also walk into any hospital and simply tell them at the desk that you have had a thought or thoughts of taking your semiautomatic weapon to a bar and shooting a bunch of people, and you will be treated to all psychiatric services available immediately (i.e., one or more of the psychiatric drugs that have been shown to be disproportionately associated with acts of violence, in addition to a bed that one will occupy for a while).
The Thousand Oaks obviously didn't avail himself of any of these services. He was undoubtedly asked by the "mental health specialist" he was referred to months earlier if he wanted some kind of psychiatric services. So what do you recommend in such a case in order to address the problem of mass shootings?