Search for a "battery" for a 2014 Chevrolet Spark at car-part.com and you'll see high voltage batteries for Spark EVs for sale. Call those junkyards (there's only a few) and they should be able to sell you the electric motor+transmission assembly and any other parts you need from that area of damage. I recommend you find a good picture of the assembly you need and send it to them (via email or text message) so they make sure to send you the assembly without taking it too far apart. Remember, most people are used to the engine and transmission being two parts and taking them apart, but that won't work for you.
The only difference between 2014 and 2015-2016 is the gear reduction ratio. If you swap an entire assembly, you need a 2014 for a 2014 car. However, if you had a 2015-2016 assembly, you could install the 2014 planetary heat set into it and it should work fine.
Note that you can't just "swap" any of the electronic control units themselves, this takes specialty tools and software to get the communication between new controller and happy again. However, swapping hard parts like the gears and motors should be fine.
Good luck, and let us know how it goes!
Bryce