[Amps] Getting a blower out of the shack

[Rick Stealey]

I have a homebrew amp with a blower mounted on the back of the chassis.  The blower has a flat flange, and the chassis has a rectangular hole cut in it to match.
What I would like to do, to reduce blower noise, is to remote the blower about 6 feet away (actually into the basement immediately below the amplifier rack.)  
I need a means of converting the blower flange to a round hose, and the compliment of that at the amplifier.  I will run the 6 feet of hose through the sheetrock wall, and down through the sole plate into the basement, so the maximum hose diameter is 3.5 inches (it will go through a 2 X 4 sole plate).  
Any ideas where to get parts I would need?

Rick  K2XT