Just register just to reply your problem, because I also want to have Nuke and AM units in SP, I have created an Afthmath.ini that enable AM units for RA1/AM etc, but no nuke from MLSO.
From Allen reply , and with the help from this guide Link, I managed to create Trigger event to be inserted into a fan made SP mission file scuXXea.ini under [Trigs]:
NUKE=2,X,0,0,32,-1,29,0,-1,-1,34,-1,-1,1,0,-1,-1,-1
Note: X= country under player control 2=USSR, 4=Ukraine
I have tested it with the file name changed to scu43ea.ini and play with my own Afthmath.ini with AM units.
And also tested it with the file name changed to scu01ea.ini and starting a new Soviet campaign without Afthmath.ini.
Both times work flawlessly with Atomic Bomb icon appear and can also have repeated Nuke strikes.
Anyway I hope this will help you, and I lastly I am no expert, someone here may have better solution than what I have, so pls reply so that everyone here can learn from you.
Edit:When I put repeatability to 1,when MLSO is sold or destroyed, Nuke will not be available even a new one is built. so I set repeatability to 2 to solve that problem, but it will cause problem to 2nd trigger action which was a "speech" so it was deleted. It work fine now and the above Trigger have being updated.