No small quantities

I bought 10l of Dulux Weatherguard Chalkstone to repaint one wall which developed a crack since I painted the whole house and used 60 litres 3 years ago. I am now short by one meter, and 5l paint is too much. You won't sell me less than 5l, I won't be buying Dulux again for sure. My Dulux shop said they can mix me some, but it won't be the same colour.