I want to Find other websites with same Google Analytics ID or Adsense ID and I had read it somewhere but can can't find the information on Google? Can someone point me to the right direction?
You could write your own spider to record the URL and adsense id. I doubt you'll find anyone giving that info away but someone might be able to sell it to you.
There are about 38.3 million websites that use AdSense. Even if you find a spider that can do the job, it will take you months to identify those sites.
I think you need to be more specific in your query like your competitors websites so that you will have a pattern to find their sites with the same google analytics id. Afterwards, implement some analysis and case studies.