There's not a way to specifically run a report of 404. What you can do is setup a fallback page in your admin section. Under Integrations there is Landing Pages. It is probably just your homepage of your site. Instead you can set it to be your homepage + a URL paramter.
Such as www.yourcompany.com?fall=back
It doesn't really matter what you set your URL paramter to be. Mine is ?get=found&utm_source=Marketo&utm_medium=Landing-Page&utm_campaign=FallBackPage
Then create an alert for yourself whenever someone reaches a page which includes that Query String. Then you'll be able to look at their Activity log on a case by case basis to see where the problem is originating.
There is no way to automate this that I know of.