Here is a template for the Southern Cross windrower ("side chute"). Again, many thanks go to Paul.
Anyone who is handy at working with metal and welding should be able to knock one of these up in no time. I am getting a local engineer to make one for me. I could have a go myself, but the end result would look a bit rough!
The engineer said he can make it fairy close to the original out of 1.5mm mild steel. However he tells me the reinforcing struts were not pressed out on the originals because the whole chute was moulded in one piece. Obviously it would be ridiculously expensive to create a new mould, so the alternative is to weld some 5mm rod or similar along the same positions and sand them back until they look close to the originals. The other things to note are the struts should be tapered off on both ends, not cut straight off as shown in the illustration, and the tabs will need to be bent down gradually until they fit the mower chassis. I'm guessing the angle of these tabs will be around 30-45 degrees.