Meanwhile, czernina is a good option if you know of a traditional Polish restaurant. The version I tried was very sour and earthy, definitely a culinary experience. There are a few places that do blood puddings or sausages too. It's an excellent choice if you want lots of iron without lots of cholesterol.
Oh, and regarding tribal sources: most of the people who knew what to do with it died before passing it on. Unlike meat, blood is a fussy ingredient. You have to use it immediately and it's a mess to handle. So it's usually left to experts. That makes the knowledge very easy to lose. Some tribes still have traditions of consuming blood in various ways, but in surviving traditions, they're more likely to wear it than eat it.