I don't think Costco specialize in organic foods. If you've never been to Costco, ask a friend, relative, or coworker to take you. Or, ask one of us here to take you in on a weekend. I shop at Costco on regular basis for their meats. The fruit and vegetable selection is limited and not always cheap.
If you take Jeffery rd and drive toward Woodbury community to the north, pass the I-5 entrance, after a few lights you'll see a vegetable and fruit seller place on left side of the street. You could check with them to see if they carry organic produce. Note: I don't mean the fruit seller at corner of Jeffery and Walnut, drive north from there.