The pads are available for a very high price. In the $20 range, each.
If you can find an automotive disc brake pad, you can make your own. I asked around my workplace and someone had a new set from a Jeep they no longer owned.
Cut the friction material off the pad with a band saw. Sand the cut side smooth on a belt sander. Use the existing metal back plate as a pattern and rough out the shape with the band saw. Two pads used about 1/2 of the material of one brake pad. Sand as needed to make the shape fit. It is not critical. Epoxy the inner pad to the location on the rear end. Adjust as needed.