A list of periodicals available for all German areas (and areas formerly in Germany) can be found at this link: https://sites.google.com/site/germandigitizedperiodicals
This site includes links to online periodicals.
https://www.stolp.de/literatur_periodika.html
http://digibib.studienstelleog.de/sdo/gak/mitt-22_01.pdf. [This file is an index to Pommern periodicals by Kreplin.