Mackerel, how to get the good stuff? I have a real problem getting good mackerel. What I consider to be "real" mackerel is that served typically in sushi bars, which I assume is Atlantic mackerel on the east coast of the USA. This fish is characterized by its strong, distinctive oily taste and large amount of brown fat (glycogen). Normally when I buy "mackerel" from "Spain", which I assume to be Scomber scombrus (Atlantic mackerel), it looks and tastes identical to sushi mackerel.

I have read that in Japan there are over 30 kinds of mackerel, but only 3 of these types are considered Saba (good mackerel).

The problem arises that a different kind of "mackerel" is frequently sold which has no distinctive taste, no brown fat, and tastes more or less exactly like tuna. I notice, for example, that one maker when it says on their package "product of Spain" it is the good mackerel, but every year around the same time it changes to say "product of Thailand", and this indicates the bad mackerel tasting like tuna.

What are the good species and how can I figure which is which before buying it (assuming I can't see it inside can)?

(Just to illustrate how tough this problem check out this fish website, it shows a picture of Atlantic mackerel (Scomber scombrus) but identifies it as Spanish mackerel (Scomberomorus maculatus)! Not even the fisherman seem to know what they are catching.)
Simple: go to your local Japanese or Korean grocer.  They will have your "good", oily, brown-fatted mackerel in the frozen section: look for or, better yet, ask for しおさば (shio-saba) in Japanese or godeung-eo in Korean.  This is invariably filleted, salted, and quite cheap.

This is most commonly served grilled, which is ridiculously easy: pop in the oven/grill for 15-20 minutes skin-side down on foil and serve.  My wife cooks this all the time, most recently earlier today for dinner!  Sample recipe in English here, but you can skip right over steps 1-6 if you're using pre-salted fish.

And for avoidance of doubt, frozen salted fish is not suitable to be eaten raw.  However, the friendly grocer can most likely tell you where he buys his fish, and in better Japanese shops may even have sushi-grade mackerel on hand.