Some 3D printer objects for coal loads can be found via TinkerCAD under the names HO coal with base 1, 2 and 3. Nothing fancy but anyone with a little 3D printer experience should be able to quickly mix, flip and resize these as needed. Be warned though that such an irregular shape takes a lot of processing and printing time. These newly painted ones look a bit shiny but I know this paint will be quite dull in day or two.

The coal texture came from an object I found on thingiverse and I have long lost the link to that, so apologies to the original creator.

Why do this? Because 160 million tonnes of coal go past my place every year to the World's busiest coal port. My grand kids expect to see coal in trains ...

Yes, wrong carriages too, ROCO and a shortened 4473.