This is the git: https://github.com/keyboardsamurai/kokoro-voice/
It claims to be able to provide Kokoro system voices to the Mac. Further as the developer seems to be uninterested in having Apple membership and provide signed installers, it likely makes him uninterested in iOS where this should work with little or no modifications (if it works on the Mac).
For the Mac... I couldn't make it speak (it can run but crashes when tries to speak) so I can't say certainly how far from usable it is, but I think I did locate the problem. When deployed from Xcode, it deploys Resources as a subfolder of Resources, while the app expects to find them in the parent Resources. However some first ideas on how to fix it resulted in further errors in the same line (still resources related, so the fix likely wasn't proper).
Anybody of better luck? This seems like something that would be a huge leap in accessibility for the Mac and potentially even for iOS.