Walther's runs their barge, apron and waterline tug boat from time to time. if one is interested in scratchbuilding, there is a book on scratchbuilding with styrene, offered by Evergreen, that showcases the construction of an S scale 3 foot gauge car float, and those techniques could easily be used in HO. I have also seen an article on scratchbuilding car barges.
I have seen an article where the barge apron was fixed to the layout, and there were several roll around carts with barges on them, so the loaded barges could be rolled away, and others could be brought in for loading, making loading the barge an integral part of the operations...
Bill Nelson