What I did was take a regular sponge with a harder abrading surface on one side.
I then cut it in half, and again in half.
For a while, I carried one of the small pieces. What I noticed however, was that I never used the soft part of the sponge, and that the soft part made the sponge hard to dry, causing it to mold.
Eventually, I pulled the two sections of the sponge apart, and kept only the hard abrasive part.
Or, if you are smarter than I am, you can buy just an abrasive pad, and cut it down to the size you want.