If all else fails, directly contacting the publisher might yield results. They could provide a link to the PDF or offer guidance on how to access it.
The first place to check would be the official website of the publication or the publisher. Sometimes, special issues or archives are available for download.
As they gathered at their secret headquarters, a cozy little cottage on the outskirts of town, they began to put together their Sonderheft. The issue was going to be a comprehensive guide to all things solar, featuring articles on the latest advancements in solar panel technology, sunspot activity, and even a few fun facts about the sun's impact on our daily lives.