I've never looked for that particular part myself. But a 98 Lincoln isn't that old of vehicle, and there were probably quite a few of them sold, so it seems like it should be possible to find that part from a recycled vehicle. It just may not be located where you live is all. You'll have to go to the used auto parts recycler place and ask them to do a search on their nation-wide network. I'd be surprised if that method didn't turn up the part you need. Try to make it as easy as possible for the used parts place, either by removing it from the car & taking the part you need with you so they can see what it looks like, or at least bring a shop manual diagram what it looks like.
Another idea, it may be possible to fix yours. It may be that the control unit is the problem & it has a broken solder joint is all. You could remove it, and if it is configured as a simple pcb circuit board, you could carefully look at it with a magnifying glass, checking for cracked solder joints and traces, might discover the problem that way. Sometimes shops will just re-solder all the joints on the circuit board, and that fixes the problem.
Yet another idea, I recently fixed a license plate light bulb wiring problem on an older vehicle, also a Ford, and the bulb still didn't light after I fixed the wiring. Bulb checked out ok, low ohms. Turned out there was a little corrosion on the bulb and bulb socket. Cleaned that off, voila. So you may have some simple problem like that, just a crusty control unit connector.