Greg, Try
Marc8_2@hotmail.com
Marc is in Ottawa and has previously advertised M37/M43 parts on this site and G741. He may not have a gate but could know a someone who does.
Midwest Military makes the tailgates and I have seen one. Not cheap but very good fit and accurate. I think if you have a decent sheet metal shop local or close, you could have one made up with the roll section around the pipe at the bottom and weld on the side angles and top box tube. If the flat sheet is a problem, just mount a tool frame on it and call it done. I think that someone carries the tailgate chain brackets and chains, may have been VPW. If you come out here, we'll look for one for you...