Got a new 2017 Volt two weeks ago and already dinged the door

... I would like to get some touch up paint to make sure the spot where the paint chipped doesn't end up rusting. Should I get the official GM touch-up paint? If so, is it a spay can, a bottle with brush, or maybe a pen? How would I find the GM part number? The color of my Volt is Silver Ice Metallic.
Or should I go with a third party paint? If so, can anyone recommend a good source that ships to Canada? Anyone know if this paint is available as a touch-up pen? A pen seems like the easiest to use on a small chip, although I might be wrong. Never had to do anything like this before on a car.
Thanks,
Harry