could you do a tear down of the usb adapter just out of curiosity I'm interested to see whats inside. My guess is a micro with protected firmware.
Ah, I was wondering how long it would take for someone to ask
It is indeed a Micro, the reason that Pico gave for discontinuing it is that they could no longer source the part. Its a Cypress CY7C64613. The other chips are a 74HCT365 and a 24LC00 (too small for the actual firmware). No parts on the back of the pcb.
[Edit] Actually, just realized that the CY7C64613 is an early member of the EZ-USB family so is ROM-less. The 24LC00 will contain PID/VID and the software will download the firmware when it runs.
I know these are still in demand as they support all of Pico's old Parallel port products. You might want to talk nicely to Pico and see if they would be willing to release a hex file to you - I can't see how it would be a significant hit to their sales by now.
One concession they did make after the adapter was discontinued was to mod their software (Picoscope 5, not 6 for these products) to support PCI and Cardbus parallel ports rather than just the motherboard com1/2 but I don't think anyone ever got another USB to work as it's a bit-bash interface. You might want to trawl through the Pico support forums to see if there is any update.
For something like a 216 it would probably even be worth keeping an old parallel port laptop (Thinkpad) to support it. I doubt if it would be worth it for the rest of the ADC200 family.
Hope it helps anyway.