For plant fans, Quail Gardens in n. SD county is fantastic, as is Balboa park and the San Diego zoo.

I'm from OC originally, but now I live in Phoenix.

Try Laguna Hills Nursery (see website) in Lake Forest off Jeronimo. Pick Gary's brain. Amazing.

In Vista, just north of San Diego, there are a plethora of nurseries.

Call them first to see if they have what you want, but try Exotica and California Tropical Fruit Tree Nursery (the latter you have to call first as it can be tricky to find - it is a house on a hill with a huge selection of tropical fruit trees - see website)

You might be surprised, but depending on what you are looking for the local Home Depots/Lowe's in vista can have some tropical fruit trees too.

These are the places I have purchased most of my trees that I am growing in Phoenix.

Good luck.

More ideas:

http://www.crfg.org/nurlist.html