Otto, what do they want a neurologist to test your son for? Clearly autism isn't usually treated by a neuro, and most health care resources are aware of this. Are they wondering if he has seizures that are contributing, which would mean that you want the neuro to do an eeg? Or do they think there is some form of brain damage or structural problem which would mean an mri or pet scan or cat scan? Until you know what you are asking the neuro to test for, it is going to be hard to figure out what the neuro is expected to actually do. It might be helpful to ask the deviancy program what the neuro is supposed to be doing/treating, and to ask them for a referral to a neuro that they work with.
I know you don't want anyone else to be hurt. Sadly, you are not going to find resources to treat him until/unless he actually does somethng to someone. In addition to that ugly realty, you are only one person, and even with 2 of you (mom and you), you cannot control a teenager's sexuality. I know so many parents who thought they could supervise their kids well enough to prevent problems and every one of them learned the hard way that they couldn't. Often they learned this when their daughter or their son's girlfriend ended up pregnant. Sexuality is one of the most primitive, driving urges that a human has. It ranks right up their with eating and breathing. All three are basic survival instincts, and at some point he is going to end up acting on his sexual urges. Not a fun thing to contemplate, given your son's sexual preferences, but it is still going to happen most likely.
If you throw away your health to keep him from hurting someone, then you are not going to be able to do anything for anyone for a long time. I know it feels like you are throwing another child under the bus, so to speak. Reality is that your difficult child hasn't actually hurt anyone, but in a few years you won't be able to control anything because he will be a legal adult. in my opinion it would be better to catch him in the act and get the police or county involved at that point so that he CAN get help. Because very few programs exist and those that do mostly need you to have committed an offense to receive treatment.
It is bassackward but it is the ONLY system we have, so you have to figure a way to play the system to get what you want. Ask the cops what would consitute an offense. Ask the deviancy program people the same thing. If you haven't had a neuropsychologist evaluation done, then go ahead and get one scheduled. That may be the info the program is needed and they are not asking for ti the right way.
I really wish I could give a better view of the realities of your situation. Sadly, this is what it is. And it hoovers mightily.