I've seen several garages on this forum with exposed ducting. I cannot find a source for this in my neck of the woods (SE Va). All that I can lay hands on is the cheap **** sold at Lowes or Home Depot and neither offer the sizes I want to use. The wholesellers might have it but I have no access to these sources. I'm looking for a transition from 14" round to 21.125"x17.5" flanged, 14" round long radius, 14" straight (approximately 12'), 4" to 12" reducer and 12" straight (another 12'). Plus, I'm looking for eight 10"x6" or 12"x4" vents that mount close to flush (or something equivalent). If you've been into a open ceiling bar or restaurant you've seen the spiral type ducting I desire. Any help would be appreciated.