As Coordinator of the Mennonite Historical Society of Alberta, we have
some archival projects online that summarizes documents from that
period which have been microfilmed. See: http://mennonitehistory.org/archives/fonds.html
Mennonites in Russia primarily lived in what is Ukraine today
(especially near Zaporozhye), but lived as far away as in Siberia
(Omsk) as well. My own father was born in Omsk to parents who were
born just West of Zaporozhye.
Judith Rempel
MHSA Coordiator
see also: Mennonite Genealogical Data Index with links to data
sources from the "Russian-period": www.mennonites.ca