
I bought a piece of high-density, closed cell foam rubber from Clark Rubber (a store chain in Australia).
Being 'closed cell' means that it is water proof so doesn't act like a sponge.
The size I used was 12mm, but it also comes in 20mm thickness.
I used the original bum pad as a template and cut the foam rubber roughly to size. Then I used a fine grade sanding disc on my angle grinder to shape it and smooth off the edges. I did this fairly quickly and in hindsight I could have achieved a better finish with a little more time.
Then I covered the whole back of the pad with thin double sided tape and attached it to the bike.
As a final touch, I gave it a coating of black wipe-on shoe wax, the kind that goes on as a liquid with a sponge applicator then dries in a couple of minutes. This made it a bit blacker and will hopefully add to the durability.
I'm very pleased with the result and it should be very easy to replace if/when it gets too scuffed.

The best part, it cost less than $5! (although I did already have the double sided tape and shoe polish)

