Was in San Diego recently and came across the San Diego Fly Fishing Club at Lake Murrary, offering free fly casting lessons to all comers. Despite inclement weather, the Club really went out of their way to help my significant other out with several fly casting lessons on the water, with loaner gear, over the course of an hour or so.
Highly recommended! It looks like they offer these lessons every Sunday from 9AM to Noon at Lake Murray. Hope this helps someone!
http://www.sandiegoflyfishers.com/activities