In my search for suitable goosenecks not a few days ago, I stumbled upon a 3D print file on cults3d. I have been keenly looking to get some parts printed as the diecast options are way too expensive. Just a drawbar costs as much as a 4x2 truck.
Here is the link for the gooseneck. Not exactly what you are looking for but I hope it can come close to it. 3D printed resin gooseneck in 1/50