Try looking around for craft shops in your neighbourhood. But I think you probably did that already. It seems there is a craft shop called Hobby Ideas in Mumbai, please check the website to see where it is http://www.hobbyideas.net/index.aspx
For a list with online shops, which ship to India, take a look at this list: http://semi-sweeties.deviantart.com/journal/Where-do-you-buy-your-clay-Help-us-make-a-list-219066658
You can also try to ask the Deco-den community on facebook: https://www.facebook.com/#!/groups/30667815752/
I hope this helps ^^