Google Officially announced, that you can now find the pages that link to 404 pages on your site.
Earlier this option was not-available at Google Webmaster Tool. Now it will be quite easy for webmasters to find who is linking to your 404 pages with the help of Webmaster Tool.
You can also download this data as a convenient CSV file. Just click on Diagnostics, then Web crawl, and then click on “Download all sources of errors on this site.”