I need to find a gear that is driven by the motor pinion on an older 4-8-4 Niagra Steam Engine.  This plastic gear also has a smaller gear around the center.  Where can I find a replacement?  Are there other models that use the same gear?

It is the favorite engine of a retired preacher that lives in my neighborhood and I would really like to get it running for him.  I have already dismantled and cleaned the motor and now need a gear.

I appreciate any help.
Thanks,