[G6Tanuki]

Copper Oxide ones are still made - as replacement parts for specialist low-voltage-high-current operations like industrial electroplating.

But they're really not that efficient - and (like their Selenium brethren) do degrade significantly with age.

Given that in the last 60-odd years we've learned a lot more about semiconducting materials and how to use them - giving rise to the likes of the Schottky diode - it's perfectly understandable that copper-oxide/selenium rectifiers have gone the way of the dodo. I am not aware of anyone still producing 'consumer' copper-oxide or selenium rectifiers, as the market-demand would be tiny!