Apologies, I thought you would have been aware of him, John Brighton;
https://steamlinesheffield.wordpress.com/millhouses/
Although I am unaware of contact details.
Mike.
I don't know the diameter of the Bachmann stub, I chuck the evil things away, but I would be very surprised if there isn't a tube suitable in the Plastruct/Evergreen range, or even Biro tubes as used by Pete Hill, and they would be a better material than 3d print stuff.
Mike.