Hi - you can buy Hypertonic Saline 10 % and 0,9 % - we don't have 3 % nor 7% - but mix the above.
For ex. Asia has 5,45 % from mixing 2 ml 0,9% with 2 ml 10%. We got 3,175 % from mixing 1 ml 10% NaCl and 3 ml 0,9%. That's how we are told to do. We hope to be able to have a ready mix of 7% but still it's not produced.
However you need a perscription for larger numebrs for both of them.