The footprint which you are using is correct. Make sure you are using proxies for scraping. I think there is a soft block on your IP by search engines, that's why you are not getting any results. You can also try the below given footprints.
Edit : Oops just now saw your second update..so you are getting the results. It's common to get inappropriate result. Just export the result and remove all the non-edu sites
site:.edu inurl:blog "Add comment" "Notify me when new comments are added" -"comments closed" -"you must be loggedin"
site:.edu inurl:blog "Write a comment" -"comments closed" -"you must be loggedin"
site:.edu inurl:blog "Notify me of followup comments via e-mail" -"comments closed" -"you must be loggedin"
site:.edu in url:blog "comment" -"you must be logged in" -"posting closed" -"comment closed" "keyword"
site:.gov in url:blog "comment" -"you must be logged in" -"posting closed" -"comment closed" "keyword"
site:.gov 'Leave a Reply' 'Name (required)' 'Mail (will not be published) (required)' 'Website' + 'Keyword'
site:.edu 'Leave a Reply' 'Name (required)' 'Mail (will not be published) (required)' 'Website' + 'Keyword'
"site:.edu" "Powered By Wordpress" + 'keyword'