Nathan originally looked into alternatives in 2008, and got as far as suggesting that the SPAL fan number VA31-A101-46A would fit, with some help.

In Nov 2010, deanhalter finished the job. The closest match is the 5.2" VA31, and the 46A variant blows the wrong way. It's the 46S that's needed.

In Dean's own words:

This fan does not perfectly line up with the Benelli part as the housings are different, but everything else is the same. Do not order the 46A, this will blow air in the wrong direction. Once I got them, I swapped the motor/fan assy to the old housing, pics in my album.

Dean's Procedure

First things first. [The housing sits between the fan and the motor body, so the fan must be removed - Ed.] The fan blades are rather easy to remove as they are just pressed on to the motor rotor's shaft. I removed the three screws from the back, chucked the housing into my vise and used a punch to drive the shaft out:

(screws not yet removed in this piccie...)

Looking at the fan, you can see the shaft in the center of the plastic fan rotor - this is where you use the punch

Once you do that, the housing is in your hands and you can now remove the rear plastic cover from the housing. It is glued in place. I used snips to clip the plastic from around the housing, then I gently pried the cover loose. The rear cover has the brushes

I chose to let the brushes collapse, then I drove the shaft through its bearing to remove it. If re-assy is your game, you just separate the brushes, replace the shaft in the plastic cover, then replace the whole assy into the metal housing with some glue. Mine is DOA however...
What I found was that the magnets had come loose from the housing and had jammed the rotor, causing one of the blades on the fan to break:

Thanks Dean