Cleaning is indeed quite easy and could indeed be done with a bit of hot water and soap. It can take a while, though.
I've heard that about the sale of these guns in the US. Presumably there's not much demand given the prevalence of better modern designs.
Over here, an original antique revolver of that period could also be posted directly to a purchaser who could hold it without a licence, as long as they weren't a known criminal. If the owner wanted to fire it they would need a licence.
I am reminded that there are a small number of modern revolvers using smokeless powder that have been converted to a loading mechanism resembling that of the mid-19th century. These are also legal here.