After going to Fry’s and striking out on finding a 5v fan, I realized that there is another source. I happen to fly RC airplanes, and remembered that many ESCs use a 40mm fan. So I stopped by a hobby store, and sure enough they had this in stock, an ESC fan from Castle Creations (an RC company):
It fit perfectly. I didn’t see CFM rated, but the fan-swept-area is larger, and it says it draws 0.16A instead of 0.06A like the stock fan, so it should be much more effective. I ended up soldering a connector between the tool head and the fan, in case I ever want to try a different fan.
I haven’t gotten enough experience with this to report an empirical result about performance. I just installed it yesterday…