My top two favorite places are O.C. Succulents and Plant Depot. These two stores have such a wide selection of pottery that there is bound to be something for everyone. Their prices are also reasonable for what you get.
There are also many other stores such as the Potting Shed By Carlisle in Orange. This store is a cool eclectic store and also sells other garden accessories. A fun place to roam when you have some time to kill or just want to get out of the house and browse somewhere.
There are also other places to buy pottery such as Green Thumb, Armstrong Gardens and Village Nurseries.