There has been talk of a GURPS India, and there have been a couple of India-like straight to pdf supplements for d20. The best treatment so far is probably Adament's Victorian India splat book pdf for d20 modern, but that deals with 19th century India under the British Raj. Expeditious Retreat put out some rather brief and expensive pdfs dealing with magic and religions of ancient India and Tibet, but they chose to conform the setting to d20, not the other way around. RQ is more versicle to begin with, so I don't see much of a problem there. An India book could dovetale into an Ancient Greece book because the tropes you find in the Ramayana and Mahabharata are essentially more powerful versions of those seen in the stories of Hercules for instance. Zeus is essentially a masque of Indra, etc.