I got mine from E bay. I would just type "slide binders" and then they come up. I got a pack of 50 amd think it was about £8 ish. But mine were plain white. They r a nightmare to put on a built corex base, I Un taped my base to put them on.
Oh dear I remember these days... I had 4 of them doing it.
Now my correx is hiden under a matt on the floor and then newspaper on top of that and they can't get to the correx. I don't have anything stopping the hay and pieces from coming out of the cage though and it drives me crazy but I don't want them eating the correx.