I'm afraid there may be bad news for your friend. I don't think that part can be bought.
My G4/450 came with its pigtail missing that little connector. I later found it rattling around in the bottom of the case. I took it back to the store when I discovered it; a month or two before the warranty expired. They looked at it and said the slot/pigtail could not be obtained separately, and they would order a whole new case! They did so (under warranty), but the case never came and never came. In the meantime, the warranty expired and the store went belly up, so that little broken pigtail is still broken.
When I bought the PB17 I just chalked it up and bought an Eirport Extreme BS with modem, and connected it via Ethernet to the G4. Hey, it works.