Look for CSA programs--community supported agriculture--if you want a drop box. Usually you have to go pick it up at a local drop location. They're popping up all over the country.
Local Harvest / Farmers Markets / Family Farms / CSA / Organic Food is a good resource for finding CSAs in your community. It looks like there are at least a few options to choose from in San Diego. Using LocalHarvest, you can also search for farmer's markets in your area and grocery stores that sell organic produce.
My SO and I are signing up for a CSA box this spring! I'm really excited.