Then you might be interested in the new accessibility checker from the DAISY Consortium.
Designed to assist content providers at any stage in their workflow, Ace by DAISY will make it easier to produce higher quality, more accessible EPUB content files that meet internationally recognized standards.
The Ace tool performs a variety of automated checks to assist in the evaluation of conformance to the EPUB Accessibility Specification and against the rules defined in WCAG and ARIA, producing a list of violations that need fixing. It also extracts data visualizations to aid the manual inspection process. Ace can be used as a standalone tool, or can be integrated as a component in broader publishing workflows or authoring processes.
“This is the tool which the industry needed to fully embrace the accessibility functionality which we’ve embedded into the EPUB 3 specification. We can now collectively move forward in producing content that enables the very best of reading experiences for all readers, reaching a bigger audience as well as meeting our legal and moral obligations.” George Kerscher, Chief Innovations Officer, The DAISY Consortium and Steering Committee W3C Publishing Business Group
Ace only runs on the command line, and you can download it here.