http://www.kustompcs.co.uk/acatalog/info_2902.html
That's what you want.
I have one in my case. You can put as many fans on each channel as you like, as long as the total power does not exceeding 17W. Considering the average fan consumes less than 2W, that means a lot of fans. (8 on each channel, 4 channels, meaning 32 fans!)
You have to cut a few holes in an empty 5 1/4 drive bay, but that's no problem. They provide a drilling template, so its easy enough to do.
Plus, its only £10...you can't really complain for that! (Y)