Two major sources of firm-level financial data for firms in India, atleast the ones that I am aware of are: Prowess from CMIE and Captialine from publishers of Captial markets magazine.
In terms of usability, Prowess scores ahead of Capitaline, however, my feedback may be biased since I have not used Captialine database since 2003-04.
Where can research students access these databases? For full time students at universities (not sure about Deemed universities) and autonomous institutes like IIMs, IITs etc. its easily accessible as most of these institutes have subscribed to either of the two or both, in most cases.
For part-time or offsite students, despite being enrolled with a university/institute (that has subscribed to the databases), access is a challenge since remote access is not permitted.
Options left are either pay huge sum for subscription to these databases or approach universities'/institutes' librarians requesting access to these databases. While most of them say No, some may permit you with a nominal security deposit and user fee.
Are there any other sources from where we can get firm-level data for Indian firms?