Working in HOn30, just as for motive power, there is no rolling stock available ready to run for a US outline layout. This is not a problem for me because building rolling stock is my favourite part - this may explain why I have 24 cars under various stages of construction to run on an unfinished layout which will only need 8 completed cars during operation!

Rolling Stock details are already on this site under the Skowhegan & Athens HOn30 layout pages, so I am just providing a link from here to those pages

HOn30 Rolling stock page 1, Methods of construction

HOn30 Rolling stock page 2, all cars under construction

HOn30 Rolling stock page 3, build a flatcar

The following images are cars which are of suitable length, and are completed sufficiently (trucks and couplers fitted, though bodies not necesarily fully detailed or painted), to be operated on the layout. See the preceeding links for further details on construction of these cars.
(NB some of the photographs were taken before the models had DG couplers fitted).