Try emailing Doug at:
fierowarehouse@comcast.net Put "Fiero Parts Order" in the subject line.
Say that Sage suggested you email him.
Give it at least a week...maybe two for a response.
He owns/owned the website that you referred to that's defunct, but he may still have a decklid spoiler or two in stock.
If that doesn't net any results, or he tells you he doesn't have any left, shoot me a pm, and I'll fix you up.
In the meantime, somebody here (the Mall) may have one they didn't get put on, or decided not to use that they'd sell cheaper than a new one will be.
Hope that helps a little.
HAGO!