Tirerack has temp tires. cost ~$60. Email or call...
Finding a place to mount it could be a problem.
Make sure tire is mounted w/ date code and tire valve is close to each other. That way the code to not buried when stored.

OE Spare Tire is T125/70
D15
I ask TR... How long should a spare last? Fiero is 25-30 years with OE spares.
Tirerack says "It is a good idea to replace the spare tire every 6-8 years."
Means getting spare from a junk car, most are too old. This shouldn't be a big shock because Normal tires expires 6-8 years too.
Check the date code on sidewall. (Same codes as normal tires.)
All 3 digit codes are too old. Junk them.
4 digit code check last 2 for year made. Older that 3-4 years, don't bother. You want some life left....
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)