Google's Mobile-Friendly tool seems to have an API, that you can use if you own/run the sites: <a href="http://searchengineland.com/google-mobile-friendly-testing-tool-now-api-access-268402" rel="nofollow">http://searchengineland.com/google-mobile-friendly-testing-t...</a><p>Or have a look at BuiltWith: <a href="https://kb.builtwith.com/lead-prioritization/finding-non-mobile-optimized-websites/" rel="nofollow">https://kb.builtwith.com/lead-prioritization/finding-non-mob...</a>