I’m terribly sorry that you are in this situation. It’s a parent’s nightmare to see a child they love headed for trouble and to feel so helpless to change it.
I do share your concern. If he has been able to fool several psychiatrists, it will be difficult to get your son into treatment. However, I do encourage you to take him to your local crisis team for an evaluation if he talks to a “blank space” and to call the police if he ever tries to hurt you again.
There is something you can do: Go for therapy yourself. Develop a relationship with a therapist who specializes in adolescent behavior and who can be both a sounding board and a resource for you. You need and deserve the support of having someone hear what you are dealing with on a regular basis. It may also be that on learning details, an experienced therapist will be able to give you some guidance about how to get help for your son.
I wish you well.