I was able to find some at CDNN sports on sale for a good price. Also, from time to time, you may see them at the Springfield store.
Regular price they are expensive, but if you will be patient, you can find deals on them from time to time.
Midway occasionally also has them on sale at a good price, but their shipping seems high unless you can also get some other things to add along with the mags.
Due to a horrible boating accident off the Atlantic coast, all firearms that I used to own were lost at sea. I will trust in our police and military forces to keep my family and I safe.