You don’t find much pickup brass at the shooting range anymore either. Used to be piles of it sitting around in bins. Now it’s gone. I’m seeing more people use brass catchers on their semi-autos too. The only cases left lying about are the steel 7.6x39 commiegun ones.
I agree with most of the comments at the linked page: put the pressure on the scrapyards. All payments are by check, purchased logged and described. And I’d point a finger at China, but in a bigger way than those comments realize: the chicoms are doing their utmost to corner the entire world’s supply of metals. Not just copper, but everything, from nickel in Norway to chromium and rare earths in Africa and SA. This is a long term strategy on their part; they’ve been at it for at least 20 years already.