Makes Tool Works sells a small 40mm fan that you can find here: http://store.makerstoolworks.com/electronics/blower-fan-24v-40x40x20mm/. This is a blow fan, so it supplies a very good supply of air. I created a mount that allows you to use either one or two of these.

First you'll need to insert the fan into the part called Fan Shroud. There is only one way to insert the fan, and it can be a little tricky to get it in. I designed it to be held in place by some M3 x 20 screws and nuts. However, in my case friction was enough to hold it in place.

Next attach the Fan Shroud part to the 40mm Blower Bracket, as shown, using two M3 x 8, or M3 x 10 screws and nuts.

Finally, attach the assembly to the X carriage using M3 x 10 screws and nuts. It may be hard to get the back nut in place, and it's not really required as long as the front on is in place.