We have them in a pond at my work, and I have caught juveniles before with a dip net. The pond is actually located inside a large walk-through tropical bird aviary. As far as I can tell them came in as free-loaders in a batch of 1000 mosquito fish we used to seed the pond back in 1996. I guess they like the sunny SoCal weather.
If you are in SoCal I can probably catch you some juveniles.