Plugin to allow post to only be visible to previous commenters

I’m looking for a plugin to allow posts to only be visible to previous commenters. Ideally it would take a number of comments that they must have previously had approved before they could see a particular post. The idea is that regular readers who are also participating would be able to view a post but not strangers. Sort of like a private post but not forcing readers to become users.

It should allow for adding people to it to start with. Maybe scan through existing comments to get an initial base of readers.

My guess is IP’s would be the way to do this.