I am particularly interested in the pentecostal groups like Pentecostal Assemblies of Canada (PAOC); Swedish Free Mission Pentecostals (SFM); Pentecostal Evangelistic Fellowship of Africa (PEFA) and Elim Pentecostals.
Today I got access to the Cadbury Special Collection of the archives of the Church Missionary Society at the University of Birmingham. An excellent if rather detailed and extensive resource. The catalogue is available online here: http://www.birmingham.ac.uk/facilities/cadbury/search.aspx
You might also look at Elizabeth Isichei, A History of Christianity in Africa (Eerdmans, 1993) and Kwame Bediako, Christianity in Africa (Orbis, 1996).