I have been searching for free/paid (preferably free) sources for postal code shapefiles for India.
Does anyone know where I can find one?
This is probabaly not the answer you are looking for, but here it is:
You won't find them, since no one (not even the Postal Department) has Authentic Boundaries.
Pin codes in India are a way of indexing Post Offices. Multiple Post Offices can have one pin code, and one Post Office can deliver to Multiple Pincodes.
It's a Myth that there is such a thing as Pin Code boundaries, which form an mutually exclusive, and exhaustive polygon coverage of the country.
Some vendors offer this data for a price, but in my experience, that data is rubbish, and wrong in many areas that I have checked.
Postal boundaries for most Indian states are at http://postalgis.nic.in/view/