Grainger won't sell to an individual direct, but they will let you use your personal credit card, and send it to your attention at your work address.
McMaster-Carr (
www.mcmaster.com) will sell to anyone.
As above, both are large industrial supply houses. Anyone in the maintenance field needs to have one (or both) of these catalogs for ready reference. And both make War and Peace look like a short story.
Another source might be J C Whitney. They sell flexible exhaust tubing.
Like yourselves, I open the garage door and turn on a fan, when running the engine for brief periods.