I found one of these http://www.newegg.com/Product/Product.aspx?Item=N82E16835119032 in my "scrounge" bin.  It seems to work well.  A couple of things to note, however:  it will only mount with the airflow reversed from stock (not necessarily a bad thing) and the aluminum case is enough thicker than the plastic fans that you must be really careful in placement to get it to go in.
The cube came right up, though, so I'm happy.