Go to any 7-Eleven in your area and if you do not see the coupon book next to the cash register go a head and ask. I did add a photo of my coupon book so you had an idea of how it looks and maybe you could show the cashier if they are lost. lol
They are only 5 dollars for 20 small slurpee coupons!
Edit: These coupons expire 12/31/2016
Unfortunately You can only buy these in person.