You have to find one and just become their regular customer.
The place I buy all my gas from is a 76 service station by my house. No pumps but they have race gas in the barrels. I've been there so many times that the owner has offered to let me buy a 50 gallon barrel at a time. And it stays at the shop with my pump on it. I can go there any time and fill up from my own barrel. This way its a little cheaper for me too.