The aquarium sponges might be like a "Mr. Clean Magic Eraser" which is actually a specific plastic foam that is equal in grit and hardness to something like a 2000-3000 grade polish.
There are such things, I've used a 3000 grade polish from 3M to restore a mirror finish on optical plastic (DVDs and CDs) with a soft polishing wheel
. But I'd expect the #3 Novus polish to be cheaper, and free from petrochemicals, which eventually attack the plastics. Should be available literally at any place that sells plexi.