Shun Mook Ultra Diamond Resonators

These equipment feet are available for more than a decade now. With all the new developments of the last years are they still state of the art? Last months I listened to Harmonix tuning feet with good results. Nevertheless I’m looking to buy used Shun Mook Ultra (or Giant) resonators but got no response.

Is that because they are still the best and everybody keeps them?
Or are they so rarely sold that there is no used market?