I suspect strongly that the radial side-discharge fan type you show from a graphics card actually works becsue the metal shroud around it and / or other card components function as air "chutes" to direct the air in the right areas. Other than that I have not seen any fan like you are looking for. The Akasa fan concept certainly is viable - it's just designed for air flow over the hot device to be by suction, rather than output pressure. I do appreciate the cost factor, though, probably because this is a very small-volume market item. Just how much space is there above each CPU heatsink before hitting the outer cover? I'm thinking there are pretty"standard" fans at reasonable prices that are only 15 mm thick, instead of the standard 25 mm thickness. IF you have that much space, you could mount one over each heatsink, and custom-cut holes in the cover over them to admit air, then include a foam dust filter outside the case top. Another option I used for a small tight case and a new fans: cut those case-top holes over each heatsink, then mount the normal fans OUTSIDE the case with their own dust filters on their intakes. This might not work if your unit actually were in a rack with other units close by, but might if you have space over the top.