The only heatsinks I've seen at princess were CPU coolers (too small) and welding heatsinks (way too big/bulky).
I've thought of the CPU heatsinks, but about the biggest I've seen is 4", the overall design works for me - but the price for a larger hunk of it from the electronics shops is pretty insane (300-500) I'd go MH before I spent 300$ on a heatsink for my 5g's lighting
Andy