I don't know of any one stop free lance artist communities. But you could try combing through deviantart. If you have a local art school in your area you could try reaching out to the art teachers to see if they have any students interested in a design project.
but also consider that there is a wide variety of artists out there and you have to make sure you find the right one.
there are vector artists
knowing the right terms may help you narrow down your search.