Today I happened upon this site, led there by this image that came up in a search.
Being a total sucker for old graphic design, I followed it and discovered a page with many links to communist and left wing publications from the past in high quality scans. Many of the linked sites belong to libraries or other collections and archives. Most of the entries are in German, with French a close second. Spanish, Italian and other languages are present, as well. There are plenty of English language entries.
I haven't taken the time to translate any of the site info itself because it is a bit overwhelming. Describing the page as "info-rich" would be putting it very mildly. But it is fun to click around, so check it out.