I got a small bottle of Silver Ice and Kinetic Blue from my dealer, wanted the match to be exact... each bottle was about $25 (I was expecting $10 like next door at the Ford dealer) so you may want to go third party.
But if you want to get the authentic stuff, you can probably find the proper code at the below link - good luck.
http://paintref.com/cgi-bin/colorcodedisplay.cgi?make=Chevrolet&year=2017&con=ky&model=Volt&rows=50