Just putting this shapefile out there in case anyone needs it later. (zip file attached)
It has the various subdivisions that the Indian Meteorological Department has divided the country into. (An eg. of what I'm talking about is available
here--it looks at the rainfall received by different subdivisions.)
Tried searching for this in the google group, but couldn't find it, so I decided to make it myself.
Just to warn you, I'm not a professional geographer or cartographer, so use this at your own discretion. . -shijith