I have a name, she is very good, but I'm not sure if her style is what you're looking for and I'm thinking she might be expensive for a start-up.
http://www.secret-agent-josephine.com/portfolio/
There is a website where you can upload your project and aspiring graphic designers will either bid on it, or work something up and you pick the one you like the best and pay for it, I can't remember exactly. Let me go see if I can find it.