Kirk is bang 0n - Radio Shack has 120v muffin fans. In two sizes, as I recall.
As to blowing versus sucking - it's not rocket science. There's a little arrow embossed on the side of the fan tht show the direction of air flow. Once I got that through my thick skull, it was simply a matter of which way I mounted it on the box.
The light tight vent I purchased from Porters Camera Store sometime in the last century. It was lying around the house collecting dust, and needed a useful purpose.