You can find high end designers on both Odesk and Elance but those ones you need to headhunt yourself. They generally have so much work that they do not need to apply for any jobs - they get headhunted by clients for opportunities. And they are picky so make sure your opportunity sounds appealing and terms are clear.

You could also try specialist marketplace for designers, there are many out there. Just do a search on Google.

Locally, go to a networking event and you'll find many, or join a Meet Up-group for designers.

You could also search local designers on LinkedIn - you can do so for free!

Finding top designers take time and effort. If you do not have the time, consider hiring a recruiter that does the work for you. You can find numerous both on Odesk and Elance.