Thanks you
I will try explaining my query again and you can correct me if the above is the solution again
1. My site has 70K pages
2. Google has indexed 500K pages from the site
Site:mysitename shows this
We have noindexed etc on most of them which is got down the counts to 300K
Now i want to find the pages that show 404 for our site checking the 300K pages
Webmaster shows few hundred as 404 but am sure there are many more
Can we scan the index rather then the site to find the ones Google search engine has indexed that are 404