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Dear Mr. Korling,
Thank you for posting your question to History Hub!
One potential resource is the Max Kade Institute for German-American Studies at the University of Wisconsin-Madison. It looks like their library and archives has a pretty substantial collection of 20th century German-American publications. The University of Cincinnati’s German Americana Collection is another good possibility. It might be worth reaching out to the reference staffs at these institutions for further guidance.
Best of luck with your research!