Also:
Garbage Days - Do some hunting on garbage days/nights. Many people put out garbage the night before, and you never know what people will throw out! (just read the forums for some stories) "One man's trash is another man's treasure!"
Colleges / Apartments - Constant rotating cycle of people moving in and out. And of course, things always get thrown out when you move! Apartments may be better consistancy, but colleges are lots of people moving out all at once. I'd say longevity for both, but apartments are spread out more during the year. (don't forget college off campus apartments too!)
Hardware stores - May be a good source of scrap, especially if they deal in appliances. The one I work in takes away the old one when we install the new one. (The owner at mine scraps them for the business, but others may not.) Also, we do get tools tossed out by those buying new ones, and returns on items that don't work! Could be a good source for someone who can get in it.
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