As someone with Asthma who sometimes uses a nebulizer, for corrugated tubing, medical supplie companies immediately came to mind. The nebulizers use small diameter non-corrugated tubing. However, vaporizers, corregated aerosol tubing…a number of different diameters available depending on the respiratory need.
Here’s one company – http://www.vitalitymedical.com/corrugated-aerosol-tubing-81344.html
The one pictured is 7/8 in diameter. Still searching for the 3/4 in (19mm comes reasonably close, BTW).