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To me the question is can he control his anger and isn't, or is he incapable of controlling his anger?

Some kids on the spectrum (Aspergers, Autism, etc) seem otherwise pretty typical but their emotion level is so high even when not stimulated that when something does happen to make them angry, they are literally incapable of thinking like most kids would (which is to evaluate options, weigh consequences, stuff that gives the typical kids self control).

Do you often see situations where he can control his anger? Or is it a case where you know that if there's certain inputs he'll always go off?

Just a thought, sometimes expecting them to learn self moderation through simple negative consequences isn't realistic, sometimes they need help learning that in different ways.

In either case, some kind of anger management therapy (yes they have it for kids that age) could be very helpful, I've talked with people who've had success with their kids with that (from an Autism spectrum point of view, but it should be easier with a typical kid).

A pediatrician could also be a good place to start, they usually have good references to resources, you should be able to get a referral to a pediatrician through a family doctor. Going that route will get you into things covered, but the waits can be very long.

Alternately since you have some coverage, you could start with a simple visit to a good psychologist to at least get some idea of what direction to go (EDIT: Even just by yourself at first to get an idea of direction). If you want you can PM me and I can send you the name of someone I've worked with in the past that I can recommend.