"Chips not available from Mouser can be purchased from a variety of sources in China"
Good luck figuring out why your code doesn't work on your "genuine" 8051.
From my experience, as soon as there is some demand (this has hit HN after all) the resellers start selling fake or inferior chips. Doesn't really matter how common or cheap they are, its just hope things work now.
Edit: when we really have to buy from China, I always create a test rig to verify component characteristics. Easy for transistors and opamps, not so easy for CPUs.
The SB card uses a number of old sound ICs that are simply not manufactured any more, and can't be bought from Mouser. Chinese shops are now the only source for these, and in my experience buying a few, they do work. No idea where they got them from however, maybe all that electronic junk that was shipped to China did get in part recycled.
It would be fascinating to find out where some of these parts come from. CuriousMarc had a video sometime ago where he got a batch of exotic HP custom ICs for his HP 9825 from a random seller in China. He first thought they were counterfeit, but after testing and decapping they turned out to be genuine.
I don't think there's any profit in cloning such rare, old chips. Even in China I suspect fab runs are too expensive to justify making old chips for a handful of retro-computing enthusiasts. I think it's more likely these are parts pulled from old boards before recycling or forgotten new-old-stock someone found in a corner of a warehouse somewhere.
In this video, someone buys a bunch of chips from various places and evaluates them, pointing out why some are rubbish, or old-but-marked-as-new: https://www.youtube.com/watch?v=k72SFBOZ_lw
Typically they are old devices that have been painted and re-marked to make them appear newer than they really are. Often they still work fine, but since they've not been retested, it's not guaranteed.
I used to think that, but it turns out there is an entire process for straightening and polishing the pins (for DIP) and repainting and labeling the ICs to make them look new after they’ve been harvested (by hand or by machine).
Good luck figuring out why your code doesn't work on your "genuine" 8051.
From my experience, as soon as there is some demand (this has hit HN after all) the resellers start selling fake or inferior chips. Doesn't really matter how common or cheap they are, its just hope things work now.
Edit: when we really have to buy from China, I always create a test rig to verify component characteristics. Easy for transistors and opamps, not so easy for CPUs.