Is there any tool of technique through which some can find from which site a competitor getting bulk referring traffic?
web ceo http://www.webceo.com/ allows you to see which of your competitors links are the most valuable. You can also use it to see what groups of links all your comepttiors have in common.
Hitwise.com and Compete.com will both show you referrers. Hitwise is expensive, and Compete has a free service, so try them first! It depends on your market though - Compete work well in the states, Hitwise work well in USA, UK and Australia. If the bulk of your traffic comes from outside those regions then you might be a little stuck!