I am trying to locate some aluminum air inlet rings, the circular rings that you can use to form round air intakes.  A couple of years ago I had bookmarked a site that sold several sizes, from around 4 inches diameter to around 5.5 inches.  Unfortunately a hard drive crash wiped that reference out, and I cannot find it again.  Can anyone please help with a recommendation as to where I can buy these annular air inlet shapes?  Thanks.
 
Jerry Fisher