None that I'm aware of. The problem is checking whether a web site is accessible is a manual operation and therefore time-consuming. And it often happens that companies break accessibility, and then they fix it, and then they break it again...
Interesting. Accessibility sounds like an important indexing signal for search engines. At internet scale companies this seems pitch-worthy to discuss building some training data annotated and building out some automated indexing engine for accessible only filter for results.
