At this present moment in time 2000 AD have only produced 4 'official' fridge magnets. There are other 2000 AD magnets out there, including the ones given away with COMIC HEROES but more of them in a later article.
I'm not absolutely 100% sure with this set but I think you could buy 3 of them through the shop but you had to be a subscriber to get the 4th. I can't remember which one was the subscriber one though as it was a while ago!
They are just pictures printed on a flat plastic material with a thin magnetic rear. Something so simple yet no more were made since these came out in 2003.
Here is Dredd with a 2 pence coin to show the size of the magnets.