I would try Amazon, Barnett, McMaster-Carr, Grainger or MSC supply. If not available from one of them, then Marcone has quite a bit of that kind of stuff in their online catalogs. Appliance Clinic also has a good amount of parts like that available online as well. If all else fails, I think you can still find a basic Broan range hood for under $50.00 at the big box stores.
