I've linked to each website's sticker request form if they have one, otherwise I've linked to the company's contact page! You don't have to send any self-addressed envelopes for these ones!
Makai Clothing (Email on the page)
Southernly Stated (Also use the code TheClassicBrunette10 to get 10% off!)
Some of these places I filled out sticker request forms, and others I simply emailed the company asking if they had some stickers so I could represent their company. I only asked companies that I was truly interested in their merchandise, because otherwise it's not really fair for the company to be giving you something.