Is there any good online shops to buy hardware components like WiFi module, batteries and all ?
Online shop for components
have a look at flipkart 
Already 
... no WiFi modules available
... no WiFi modules available
You mean this ? D-Link DWA-525 Wireless N 150 Desktop Adapter Network Nic - D-Link: Flipkart.com
Search on eBay too
Search on eBay too
Already
What kind of module are you searching for? PCI, PCI-E, USB?
I was looking for something that can fit into my Zync Z930 tablet...which disappointed me with its poor wifi antenna and weak battery