Hi Fran . . . I don't know where you are in Washington State, but here in Vancouver, WA we have RV Pro, an RV parts & repair place that I'm pretty happy with. Their pricing is about the same as shopping the Internet, they have a thick catalog of parts they either have on-hand or can get within a day or two, and on the one occasion when the City Water connection I bought from them leaked, they swapped it for a working one.
The Belly Band is a standard aluminum extrusion, something you can order from a metal products supplier and (carefully) bend to match your trailer. Ask around, see if you have any friends that build or repair airplanes and they should be able to show you how to bend the stuff without disforming. If you have the old one it's probably easier to remove, strip, polish, and re-install it.