Free Oculus Icons and Illustrations
Free Oculus Icons and Illustrations is a free Illustration design resource made by Dribbble user Tanner Christensen. As far as I can tell, its license is Creative Commons Attribution-NoDerivs.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.