I have actually seen the flyer for ANTIFA, and the black nationalist groups. The flater falls under the Racially and Ethnically Motivated Violent Extremism, the former under Politically Motivated Violent Extremism.
Those flyers come out as CUI, or higher, so I'm not posting them here, you'll have to take my word that they exist (or not). If I were to hazard a guess, I'd guess that they don't get leaked (or reported on) because they won't get the rage clicks flyers like the one linked above reliably get. Or maybe they do, just not the parts of the internet I frequent.
The FBI has certainly lost some credibility and become more visibly partisan in the last couple years, and it is smart to keep a jaundice eye on any organization with that much power and weapons, but part of that eye is a realistic view of the things you're looking at. For example, American Contingency was not identified in that flyer as an extremist. They were actually labeled mainstream. What it said was that actual extremists may self identify with that site, which is a very different thing.
Keep a close eye on the .govs attack dogs, they need to be watched, but don't ascribe things they aren't doing. Boy, Cry Wolf, and all that.