If I’m not wrong, VR sells data. There are other MF data providers like Morningstar, CRISIL, Accord, Dion, Ace MF etc. But to answer your question, the source data is disclosures from the AMCs. These guys aggregate the data and sell it.
@VijayNair , not sure if Valueresearchonline uses them or not, but they do have very good research database regarding Mutual Funds -
Products intended for Mutual Funds / AMC
Our financial products of Equity and Mutual Fund applications help the Mutual Funds / Asset Management companies to carry out the desire research and helps to take right business decisions.
There are few other such companies as well, which provide the database necessary for doing such research work.