This I guess
http://mayflash.com/Products/PLAYSTATION/PC001.html
Controller talk:DualShock 2
With Dualshock 1 and 2, I'm guessing this is far more popular hardware: http://www.dx.com/p/789
If you search for converter in ebay or similar, 99% of results are that with exact same hardware (http://www.ebay.com/sch/i.html?_nkw=PS2+controller+to+USB), but maybe bit differend packaging. I had one of those earlier, one bit differend now and they also work directly with Playstation 3 because of standard DirectInput.
But like said, almost all of those have differend kind of packaging or branding or none at all. One I have now installs as two "Twin USB Joystick" DirectInput controllers, HWID 0810:0001.
As there are so many differend hardware and hardware is required because of proprierary connector, just link user to DS3 article if they have compatible converter or controller article for generic xinput wrapping.
Ah, nice find. And yes I am aware of sillyness required to make them work, but wanted to make stubs for now at least.