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With shops its iffy because I'd assume they get them with product and give em out - sometimes they have them, sometimes they don't. You're best bet would be to join the STICKER CULT and look at the list of emails for companies - you send a company an email with your address asking politely for free stickers, and chances are they send you one back and in a week or two you get an envelope with stickers inside!
I'm pretty sure I'm a leader in the Sticker Cult, so I can let you in if you want in. Emails and SASEs are the way to go for free stickers.