As already mentioned by Mohan bhai, in the case of stocks, these IV values are calculated based on the stock options. Every individual strike has its own IV and that is systematically combined to get the Weighted IV Value for the whole stock. Some people mistakenly thinks that it is the IV of the Equities/ Stock, but in realty, it is all based on the options of that particular underlying stock.
In Indian Markets, there are a few vendors which provide such information, like - FinIdeas, Myfno, Greeksoft.co.in, Nest Options Trading Suite from omnesysindia etc. But non of them is free.
pannet bhai, I am not totally sure about it, but there are some tools / modules available within Matlab / R / Stremabase etc. which can calculate the Option Greeks etc. in real time, provided you have the required real time data for all those respective option contracts etc. Maybe some senior member can throw some light on this. The vendor names that I have mentioned above, must be using some similar tools in order to calculate the real time greeks, which they then display within their platforms to the clients.
Thanks and regards