409 is/was an older model. I believe Beretta started making them in the 30's and replaced them with the 410/411 models in the late 50's early 60's. That was replaced by the 626 models which was then replaced by the current 471's.
As far as any for sale, the usual sources; gun broker, guns international etc would be places to look. You might also check Shotgun World .com as well.