Getting random users

I have a website that I use as a comment exchange. Right now a lot of the work has to be done manually, because I can’t quite work out how to make it do the following below.

I want to be able to generate a set number of random users for a user to comment on and have that emailed at a set time. I also want to be able to include who that user is also going to get comments from.

For example, if there was custom fields, that could somehow pull a random number of users every set time (say weekly or whatever) and then I could mass email users. While, it also could detect if the first user had been selected by other people and have it as the comment from..

At the moment I have members managed as users, and have to use excel to generate them randomly, then search, copy and paste who they have comments from.

Nothing like this really exists so if anyone has any ideas that would be awesome. 😀