Assuming you do not find a round fan, Would constructing an adapter be possible? Just a box large enough to hold the new fan and mounted to the ceiling over the round hole.
My 30 Year-old Bathroom Ceiling Fan Has A 10 Inch Diameter (round) Vent Into My Attic. All Of The Replacement Fans Have Square Mounts. I Can't Cut The Ceiling To Fit The Square Fan. What Can I Do?
Go to a plumbing or electrical supply store or a kitchen equipment wholesaler and ask the same question of the people working at the parts counter. Architect have catalogs of all the manufacturer's product lines. They might take the time to look through their copy of the Sweets Catalog for exhaust fans being sold.
You could place a new unit above the existing installed box in the attic space. You would have to construct an air tight and insulated enclosure to encase that new fan.
You could place a new unit above the existing installed box in the attic space. You would have to construct an air tight and insulated enclosure to encase that new fan.