Hi @monkjoe77,
I believe as things stand right now, if you select the anonymous discussion option, there really isn't a great end-user way to identify who made the posts. I think this is very likely a deliberate decision to enforce the anonymity, as there could be issues with calling something anonymous only to have students learn their posts were identifiable. With that being said, I do believe someone has said in the past that Canvas Data 2 *might* have identifying info available, but that's something you'd need to work with a Canvas admin to have setup and access for you, and that may be something your school/institution won't have resourced to actually do (especially for just a one-off scenario like this.
I think for now having the students copy/paste their posts to an assignment or something would be the better solution.
I hope this info helps!
-Chris