WANTED: BACKPLATE OUTLET for Standard Time bell

Hello, I have a Standard Electric Time
MAJ-6 bell that is missing the plug socket in the baseplate.

Does anyone know where i can find that piece, or a Standard Time bell backplate that would have it, please?

I tried one I have, but its smaller than the opening in the backplate.

If the Fire Alarm Forum folks know where i could locate this, or what i could use in its place, I’d be very grateful and thank them.

Ed Burmett