Pampers premium nappies size 6

I am a mother of a 18 month baby boy who weighs 21 kgs. I have been buying the Pampers premium nappies over the few months but there is no longer stock . Has the size 6 been discontinued? If so, is there an alternative that has been provided? I haven't received these nappies since September and have resorted to buying the normal size 6 which is quite tight to the baby.