Thank you for that link, Andrew,
I tried a web search but didn't find anything that good.
I posed my original question to a contact who is mid-career as an avionics engineer - his response was to send me a link to the precious metal recyclers he uses when needed!!!!
The big irony was that their address is just down the road from where I was last employed, miles away from where I live now. Shipping would probably render such a deal profitless!!
Then there are the 400-ish dead 3½" hard drives I still have. They're what's left of an original eBy job-lot of 1000+ !! I was dismantling them a few at a time and weighing in their chunky bits locally. However, that's a labour-intensive pursuit and, having reached the ripe old age of 85, I realised there are better ways of spending my time.