How to get an empty 2006 iMac box?

Hi people, I am selling an old 20" 2006 polycarbonate iMac on eBay. i want to buy a box to increase its value. Does anyone know how I can get one of these boxes. I don't really mind if it doesn't have the polystyrene or if its the 24' box. Preferrably under £25.

Any help appreciated.

Thanks MBA08