Element14 (farnell outside india) in.element14.com
Future Electronics Inc. futureelectronics.com
Mouser electronics in.mouser.com
RS Components in.rsdelivers.com
Except these there are hundreds of small online sites selling components and modules which these cant provide and 50% or more cheaper than those distributers.
Also in ebay.com , amazon.com, amazon.in, ebay.in you can purchase popular microcontroller based modules mother boards or daughter boards like arduino and raspberry pi .
sparkfun and adafruit deliver in india but they cost more as they receive payment only in dollars.