Yes, there's graffiti in Irvine, it's just a little harder to find than in some other places. But the directions that I found on the web were accurate, and led me to a storm sewer under UCI that's filled with art. Photo gallery here.
Also, if you have any interest in street art, you need to see Exit Through the Gift Shop. It's still playing at the local art house movie theater here, a short walk from of all this graffiti. Whether it's all true, an elaborate send-up, or both, it's very entertaining.