If you cannot remediate an inaccessible document from a copyright-protected source, you can request an accessible version from the original publisher. Below, please find boilerplate language that you are welcome to use in your request email:
Dear Publisher,
I am an instructor using your materials in my courses. Federal and state regulations require that all digital course content meet WCAG 2.1 Level AA accessibility standards. The attached documents do not currently meet these requirements.
I am requesting accessible versions of these materials by [provide a deadline]. If you are unable to provide accessible versions by this date, I will need to seek alternative resources.
Thank you for your attention to this request.
Sincerely,
[Your Name Here]