Hei,
Unfortunately there are no FBO as such yet in India.
You could contact the state run Indian or Air India (soon to be merged I believe) who do handling for foreign customers would be the easiest.
I do not have Tel Nos. sorry but ma be other prruners might help or contact the Indian (airlines) office in Sydney and they might be able to pt u on to someone.
Can't help with Karachi
Regards