Yes - DSC can be bought online by NRI, Foreign Citizens, and Foreign Companies. DSC are used at multiple websites that involves establishing your identity during a transaction in India.
For example, Ministry Of Corporate Affairs (India), DGFT, Trade Marks, & Patents, Bidding for Tenders from Government of India - they all need DSC issued by a licensed Certifying Authority.
Buy your DSC from
dscexpress.com or
dscsignature.com