The only advice I have is the advice my counselor gave me. I was married to an abusive alcoholic, and here are some of the things my counselor has taught me over the past couple of years:
~ Your job is to provide a stable, healthy environment. Children, and adults, tend to choose that and live what they see modeled in a healthy environment. I have a 12-year-old who sounds similar to yours -- with anger management problems and depression (which in some people expresses itself as anger). What we've done (me and my new SO) is to model for her that which she never saw when she grew up: Anger handled properly. During my marriage, I didn't show my anger at all; I stuffed it. And my AXH exploded. So seeing two adults get angry and handle that in a proper way has helped her. Just as seeing us react calmly to her provocations has. It's like she's trying to see "If I do THIS, will you explode? If I say THIS, will you tell me I'm an idiot and you hate me?" because that's what she's used to from her father. When she's faced with firm boundaries established in a calm manner, it calms her down.
~ It's important that they know that they didn't cause it. Kids think they cause all kinds of things. My kids both thought their father drank because they were "bad." It's taken a long time of repeat explanations to drive the point home that this is a disease (psychosis may be easier to accept as a disease), and like with all diseases, if the sick person refuses to get treatment, they're not going to get better.
~ They will have mixed emotions. When it's your parent we're talking about, they will somewhere always have that hole in their heart where their parent couldn't be the parent they wanted. The point you want them to get to, however, is past "My mother never loved me, there's something wrong with me" to "My mother never loved me, there was something wrong with her"...
When you're in a small place, finding a good counselor can be hard, and then there's the fear of the stigma -- being 12 is hard enough without being The Kid Who Sees A Therapist. I agree, though, that driving to the next town (if that's an option) could definitely be worth it. Where I live, Ala-teen meetings are few and far between, so we've gone the counselor route, and that has worked well for us.
I also let my kids vent. I don't ever speak badly about their father, ever -- but when they say things like "Dad is lazy, when we're at his house, he just sits in front of the ballgame with a beer" or "I hate Dad, he's such a loser"-- I let them. I don't correct them, I don't explain the behavior, I let them talk about what they see. I ask, "so what do you do then?" or "how does it make you feel when he does that?" and sometimes they have an answer, sometimes they don't.
I think for your sanity (it sounds like you're a primary caretaker for this boy right now?), I would recommend finding some good reading material that talks about what living with an alcoholic parent does to kids. Maybe hang out in the ACOA section of this forum, too, and see what you can learn there. I can't pull a title out of my brain right now, but I'm sure others will come along with ideas.
This boy is lucky to have you -- because living with an alcoholic messes with your mind, and the fact that you realize this and are reaching out to find ways to help him is awesome.
Edit to add this: Calling AA's helpline is a great idea because they may also be able to recommend a counselor that's not too stinkin' far away...