If you could find a used Mirage 14" x 4.5" steel rim at a salvage yard, that would be my first choice. I use different width rims on my Mirage, but I do them in matching pairs on each axle. It probably wouldn't make a big difference to use one rim different from the rest, however.
I have
four 14" x 4.5" Mirage steel factory rims,
two 14" x 5" used G4 factory steel rims, &
two 14" x 5.5" after market steel rims.
I prefer the narrow 4.5" rims (less weight most likely), but the 5"/5.5" wide rims work perfectly fine.
Most common steel rims for a Mirage -
14" x 4.5" * = recommended tire widths of 145-175 mm
14" x 5" ** = recommended tire widths of 155-185 mm
14 x 5.5" = = recommended tire widths of 165-195 mm
* factory size
** nice size rim for possible tire options below
Most common 14" Mirage tire sizes -
165/65r14 = 22.4" outside diameter
175/65r14 = 23" outside diameter/+2.7% variance
185/60r14 = 22.7" outside diameter/+1.3% variance
Less than 3% tire variance is considered very acceptable.
If I were in your situation, I would do the following -
1. Try to find a used 165/65r14 Mirage steel rim from a salvage yard.
2. Buy a matching pair of 14" x 5" aftermarket steel rims & use them together on the same front or rear axle.
3. Buy one 14" x 5" steel rim & use it with the other three 14" x 4.5" factory steel rims.
If I ended up doing number 2, I would use my extra leftover 14" x 4.5" steel rim as my new full size spare tire. Next time you buy new tires, keep one of the old tires for that rim & use it as a full time spare. A full size spare will fit in the wheel well (may stick up an inch or two). I like having a full size spare for longer trips. I wouldn't want to travel a long distance on a donut spare tire & finding a 165/65r14 replacement tire in that type of situation is most likely not going to happen.
I've canned the donut spare tire & carry a 165/65r14 full size spare tire 24/7 now.