If someone has not read a book out loud and recorded the book for "audio" use as an audiobook then that process needs to be done.
Or the text must be available to process/scan and then be converted into audio format.
The starting point then being some scanner that scans in the text from a physical book and then, in turn, the text is converted to some form of audio format.
Step 1: scan the book pages into electronic/digital format.
Step 2: convert the digital format into audio.
There are any of hand held scanners that can be used to scan book pages. And there are also automated scanners that require that the book be unbound. However, there are also scanners that will flip book pages and scan page by page. Likely expensive.....
How do you envision the process being done in your environment with your requirements?
FYI (Not a recommendation or endorsement for any given product):
View: https://www.youtube.com/watch?v=M_xxuwxVUOY
You can easily find other similar and related links regarding going from book ---> text ----> audio.