If the crate itself is 48" x 30" you should be able to order a metal pan from several sources. But, if your pup is ripping up a plastic pan I bet he will continue to try with a metal pan and the sound of toenails scratching on metal will drive you nuts.
What about cow stall matting? It's thick, durable, will scratch but not right through for a long time, and his scratching on it will be quieter. A TSC or Co-op might be able to help you. You need to have it cut very, very snug so pup can't get a corner up.
Like this: http://www.tractorsupply.com/rubber-...-6-ft--2219003