For those with Mennonite or even Amish ancestors in Pennsylvania the Pennsylvania Mennonite Heritage Illustrated Quarterly might be of interest. It is available as part of a membership benefit to the Lancaster Mennonite Historical Society. You can also check out back issues through indexes available on the website.
According to their website, the "Pennsylvania Mennonite Heritage focuses on historical background (Europe and America), religious thought and expression, culture, and family history of Mennonite and Amish-related groups originating in Pennsylvania. Additional features: Genealogical tips, readers’ ancestry, queries, Pennsylvania German dialect stories, and book review."
The predecessor of the Pennsylvania Mennonite Heritage is the Mennonite Research Journal. Published between 1960-1977, some issues are available for purchase. You can see a list of some article from previous issues on the web page for the Journal.