I also wish they made that adapter. We're using legacy-type database software that can only print to a parallel port. But our new printer just has a USB port.
We can't use that printer unless it can be converted to parallel.

I looked a bit more, and from what I have seen, this is impossible to do. It seems as if you need a USB controller to access a USB device in any way (even through a converter). Therefore, your motherboard either has to have native USB support or you need a PCI add-in USB card to access USB devices. (Apparently there are tons of USB PCI cards that you just stick into the PCI slot of a pre-USB machine (even if your motherboard doesn't support it) and you have instant USB ports).

Apparently the reason you can find converters the other way around is because virtually all motherboards can handle serial and parallel devices and it's simply the means of connection you need the converter for.

Please correct me if this is wrong? I did a whole bunch of looking and looking and it seems this is the conclusion I've come to.

It doesn't exist. It can't. You can find adapters that will adapt a USB port to serial or parallel easily enough, but the signal output from a parallel port (and the software that drives it) is not set up to handle the demands of USB signal management. What you can do is get a PCMCIA USB card and do it that way.