don't know if this one has been posted before, but this weekend ik stumbled upon this website by fans about 1950', 1960's & 1970's carboard models published in the former DDR:
Kranich Modelbogen
this is a website by fans for fans, and it has downsized images of the modelsheets.
as i'm not a specialist in international copyright laws, i really don't know if this website is a pirate site or not (models were published by the government, they're more or less 50 years old and the scans aren't in the original size). i do not know if any of these models have been republished recently, but most likely some sheets are still available on auction sites.