Usually fired/not cleaned brass at gun shows by the bag....not lately!
At the local indoor range, I keep an eye out for neighbors shooting what I like to reload who are not picking up. I ask if I can pick theirs up and not only do I usually get a 'yes' but many times they help.
Some look at me like I'm crazy.... Yeah, crazy like a fox; Free brass!
Also, at the local shooting hole on BLM land, I look for "glory holes" of brass. Last weekend shooting 5.56, I found a shooting spot with a ton of new looking, I mean shiny, .45 Winchester brass!!
One good thing about the Jonny-come-lately's is they leave perfect brass laying around every time they shoot. Me, I scrounge everything reloadable up and give away what I don't want to a buddy.