The flag of the "Euro-Asian Youth Union" was found It consists of an eight-arrow gold cross on a black field, the star of Chinghyz-khan
The organization calls itself the "new oprichniks". "Oprichnina" was the official state terrorist organization created in XVI c. by Tsar Ivan the Terrible in the struggle against feudal lords (boyars). Their symbols were the chopped off head of a dog and a broom (to find enemies and to sweep them out). Their motto: The Word and The Action! (Slovo i Delo). The organization is traditionalist, counter-revolutionary and turkophiles, but not neo-nazi.
An image of the "unidentified black flags" that I sent you a few months ago. Finally, I identified it: it's the flag of the Eurasian Youth Movement or Union.