This is a link and pin coupler that is compatible with LGB bogies.
www.thingiverse.com
I have compared them to LGB ones and they look similar.
The pin print leaves a bit to be desired but can easily be replaced with a split pin trimmed to size.
Link and Pin G-Scale Coupler by FatFarlake
This thing was made with Tinkercad. It should fit on any G-Scale model that have LGB compatible couplers. I had the best result with ABS.
www.thingiverse.com
The pin print leaves a bit to be desired but can easily be replaced with a split pin trimmed to size.