Searching a catalog or database by Subject Headings is one way to quickly amass resources on your topic.
Below is a list of Subject Headings associated with Radical Reformation/Anabaptist studies:
Grace (Theology) -- History of doctrines ;
Infant baptism -- Early works to 1800 ;
Nonviolence -- Religious aspects -- Christianity;
Indexes comprehensively scholarly and non-scholarly journals in religion and theology.