May I recommend a google search with 'Korrekturzeichen' and another one with "Korrekturzeichen download", and you might find what you're looking for.

Hi, Melanie. At the risk of insulting you with an "obvious" remark, do you realise that Duden itself usually includes a section called Korrekturvorschriften , including the wichtigste Korrekturzeichen.

For example, in my 21st edition, volume 1, the section begins on page 79.