First thing you want to do is make an account if you dont already have one on www.usps.com.
But in case you do not know exactly where to get them so iv'e provided the link:https://shop.usps.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10152&storeId=10001&categoryId=13354&productId=11655&langId=-1&WT.ac=11655
and these are free so dont worry about paying money.
and also take about 7 to 10 days to get them and its worth the wait.and you can also go to get smaller stickers.
go to the postal store,shpping, priority mail,veiw all,stickers..BEHOLD!!!!