I worked on a project for one of the big registars and even they didn't have a proper whois api!

Most use cases of APIs into whois data are sketchy (typically email spam).

Not an API, but perhaps a good basis for one: https://github.com/secynic/ipwhois

Whois data itself is also somewhat suspect in general. It's best effort, not required to be correct in any way.

Check out http://whoapi.com