shams:
adafruit motor shield library
adafruit motor shield v2 library
Neither of those libraries contain a file named Motor_Shield.h
shams:
and this one i added manually to the libraries folder after downloading it from the net
motorshield-master
Post the link to where you download it from. Use the chain links icon on the toolbar to make the link clickable.
I'd think that the company that provided you the code would have either included the library with it or documentation that tells you where you can download the library from.