Duplicate Comment Spam – new development

Recently my website veryserious.org has been beset by spambots that scraped existing comments by real users and copies them. This is smart because of course the 1st comment has already gotten by akismet so it’s a good place to start when copying.

Has anyone else seen this happen? Are there any plugins specifically for this problem? I found some anti duplicate comments but those were for bots flooding the same comment, this is flooding with duplicates of actual comments.