come by vs get one's hands on

come by

• To obtain; to get, especially by chance or involuntarily. 

• To come near to; to pass; to visit. 

• A command to a sheepdog to move clockwise around the sheep 

get one's hands on

• To get; to obtain; to secure. 

• If you can get your hands on the right ingredients, it's an easy recipe. 

• To catch.