If you have the funding, "rent" one. There are lots and lots (and lots) of decent designers to choose from, and one person's Rockstar is another person's decent. Designers should be much, much easier to find on-sight than good developers. You have a whole world of their work in front of you. You only have to contact them directly and tell them that you are impressed with their work in (insert some site, etc. here) and wondered if they would be willing to consider being competitively reimbursed for a small amount of their time. Then try to close the deal by stating your problem (what you want them to design) briefly without flowery language or sales-gibberish, spelling out what you need their work to accomplish (e.g. Our product/service is X. Our target markets are Y and Z. The different types of users using our site are A and B. A needs to do C, D, and E and B needs to do F, G, and login to do H, and I. And the best way to do this is by hiring a good designer to talk with them to find out what they would want to hear from a startup looking to hire a designer for temporary work. After you get the designer hooked for the work, keep using them and try to get them to come on full-time. If they don't, you at least have a design to attract other designers.