My joke is always that I can build anything but don't ask me to decorate it! Are you looking for a "designer" or a "decorator"? They are different. Do you have a budget in mind? (Designers will typically kill it on the high side). Do you have a style you like? (See if your designer has done anything like it)
Review their past work carefully INCLUDING the project costs for each outcome.
You can locate designers in CraigsList and Angie's List. Anybody in a local home magazine or newspaper will inevitably be pricey. The OC is not exactly cheap living to beg with anyway!
Here is a good overall article to help you get a feel for the search.