Spare Tire problems of the 1998 Saturn SL2

My firestone compact spare tire for a 1998 Saturn Sl2, which has never been used, shows tread separation. The rubber is splitting apart in the tread area and the belts are showing through. This also happened to a previous firestone compact spare I owned for a Saturn. The tire is size t115/70r14 and the serial number is hym7h5a377. The tire is admittedly old, but the extent of damage is alarming considering the tire has not been used. It has been impossible to find a new replacement- tire dealers say to get a replacement from a junk yard, but they would have the same problem. A full size spare will not fit in the trunk's tire well.