I was wrong in my original post, Vortex II not IV has 3 speeds and reverse --- Sorry.
I bought mine from Amazon for ~$60 about a year ago...mine is 9" blades single speed part number 90043-CR. It works very well for us and we didn't need reverse, but since you want reverse you need the Vortex II, not sure the part number.
These fans are availabe everywhere; Tweety's, CW, Amazon, etc.
Very easy installation, all from the inside, and good air flow for the $.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)