Is Google Docs spell checker available?
I have tried MS Azure - but it's not as good as I need.
No, there is no API which gives visibility to Google Docs spell checker.
In the past, there was an unofficial, undocumented API that was hosted by Google for spell checking, available at http://www.google.com/tbproxy/spell?lang=en.
This has now gone and there was never a replacement released. You can see remnants of its history by doing a Google search for this URL.
As per Stack Overflow guidelines I can not recommend you a spelling checker API for reasons of bias, though you can find plenty paid and free APIs by searching the web yourself.