I have published a history of The Russian orthodox Church in the 20st century (Shumen, 1997) and I am finishing a general history of the same church. Here are some titles in English:

Luukkanen, A. The Party of Unbelief: The Religious Policy of the Bolshevik Party, 1917-1929. Helsinki, 1994.

Chumashenko, Tatiana A. Church and State in Soviet Russia: Russian Orthodoxy from World War II to the Khrushchev Years. Armonk (NY) - London, 2002, 235 p. (The New Russian History)

Jane Ellis. The Russian Orthodox Church: a contemporary history. Bloomington, Indiana University Press, 1986.

Pospielovsky, D. A History of Soviet Atheism in Theory and Practice, and the Believer. T. 1-3. London and New York, 1987-1988.

Wynot, J. J. Keeping the Faith: Russian Orthodox Monasticism in the Soviet Union, 1917-1939. College Station (TX), 2004.

Fletcher, W. C. The Russian Orthodox Church Underground, 1917-1970. London and New York, 1971.

Stroyen, W. B. Communist Russia and the Russian Orthodox Church, 1943-1962. Washington, 1967.

Konstantinov, D. Die Kirche in der Sowjetunion nach dem Krieg. Salzburg, 1973.

Fletcher, W. Religion and Soviet Foreign Policy, 1945-1970. London, 1973.

on BG:

Antonoff, Nicolas, Marin V. Pundeff. Bulgaria: Church and Religion. New York, Mid-European Studies Center, 1951.

Slijepčevič, D. Die bulgarische Orthodoxe Kirche 1944-1956. Muenchen, 1957.

Fessen, Friederun. Das Verhaeltnis von Staat und Kirche in den europaeischen Volksdemokratien Albanien, Bulgarien, Jugoslawien, Polen, Rumaenien, Tschechoslowakei und Ungarn (Diss.). Leipzig, 1959, vi, 247, 39 S.

Beeson, Trevor. Discretion and Valour: Religious Conditions in Russia and Eastern Europe. London, Collins, 1974, 286-299.

Christ is risen,
Fr Pavel