My pharmacy is also having a difficult time locating 3% vials but did locate and stock vials containing 15L with instructions to pour only 4ml into nebulizer. I use one vial 2x a day. I have however wondered if reuse of the vial is sterile. Not sure about making your own but again the importance of a sterile solution shouldn’t be discarded. I wish you luck in locating 3% for the benefits of its use is most helpful.