The ignition system will generate a spark without the computer. If you have no spark, you have other problems.
Computers seldom fail, usually it is a sensor, wiring or actuator that has failed.
There are no new FORD OEM computers that are compatible with your car. Everything you will be able to get that is a direct substitute for your current computer will be a used unit.
1989 MANUAL A9L, A9S
1989 AUTO A9P, A9T
1990-92 MANUAL A9L
1990-92 AUTO A9P
1993 MANUAL A3M
1993 AUTO C3W