I learned about the availability of the Google Material icons via Twitter. I saw a tweet where these icons were offered as a download. Normally I like to go the the official source so I found the following page: https://www.google.com/design/icons/
On this page you can find the Material icons Google offers, you can choose the size and background colour and then you can download the icon in svg, pngs or use it in CSS. A developer guide is also offered and there is a Github repository. The icosns are available under the CC-BY licence. You can find the specific pages here:
{fa fa-code} Developer guide
{fa fa-github} Github repository
{fa fa-book} CC-BY licence