Just like you I did some online search and didn’t find anything, unless I’m looking on the wrong places. Could your client be interested in audio books? There are thousands from which you can choose from online. Hopefully someone else can give you a better answer. I hope this helps.
Have you talked to anyone at the National Library for the Blind and Visually Handicapped? (I think that is their title). It is part of the Library of Congress. Librarians are a wealth of information and love to share. (I worked in libraries for 10 years). They may know of resources for what you want. And if you have trouble finding what you want on tape some libraries will create recordings for the visually impaired of things that don’t have a large market. I was a volunteer recorder for the blind back in the late 70s, and I remember doing things like knitting instructions that people would bring in to be recorded. I rather imagine the technology is pretty different now 🙂 Good luck.