Purchase stickers through an online store such as Ebay, Amazon or iOffer. Individuals post their extra Rockstar stickers for sale on these websites. In some cases you can bid on the price while other times the price is set. You will also have to pay shipping to the individual selling the item.
Find Rockstar stickers at local motorcycle and motocross stores. These stickers are available because Rockstar sponsors a number of X Game and motocross sports and events.
Buy Rockstar stickers online through the Rockstar store. You will need a credit or debit card to make such a purchase and you'll also have to pay additional shipping costs.