You can get castable polyurethane resins in very high hardness,
like rollerblade wheels for example. Just make sure you get a
high-strength resin, not a mold-making resin, and take care to
ensure that it's low viscosity before cure. You'll need a vacuum
chamber to de-air during casting.
More resins are available if you can handle a UV or thermo cure
instead of RTV (room temp) - these are more common in commercial