Is there any 3rd party API which will provide text to speech facility??
Yes.
The CMU Flite (Festival Lite) speech synthesis library has been ported to iOS and appears to be used in many iPhone and iPad apps in the App store.
Yes. Follow this link for your reference. You can use this as you require. There is iPhone sample in there, but it is easy to convert it to iPad.
And there is also other way with google api using following way.
http://translate.google.com/translate_tts?tl=en&q=Yourtext. But it has certain limitation like 100 chars and also you have to look for commercial usage conditions.
This you can load in UIWebView passing your text.
Hope it helps.