If your pulmonologist did not already recommend airway clearance, they are not up-to-date in managing MAC and Bronchiectasis.
That is not uncommon and not an indictment of your doc. Even though it doesn't seem like it when you are reading here, MAC is a rare disease, affecting fewer than one in 1000 people. That means even a pulmonologist may see only one or two cases per years, compared to hundreds of cases of Asthma and COPD.
It is in you best interest to find someone with experience to help you on this journey.