I need advice on finding research sources in Russia, concerning Ferenc Migray. He participated in the leftist government of Bela Kun in Hungary (1919). After Kun's fall, the rightist government from Admiral Horthy persecuted their opposition and Ferenc Migray had to flee to Soviet Russia, where he stayed during 10 years. As a side note: Ferenc Migray's brother, named Jószef Migray, was minister of agriculture of the Bela Kun regime (People's Commissar for Agriculture).
I believe Ferenc Migray's stay in Soviet Russia corresponds approx to the period late 1919 and 1929. After this he emigrated to other country. Please, where can I find household registries, residence permits or sources of research to find more information of foreign residents in Soviet Russia during 1919-1929? Any advice is welcome :-)