In addition to the plants you listed, juniper is also a main host of this type of rust (caused by 7 different Gymnosporangium species). Different species of Gymnosporangiums rusts can have different hosts, but azaleas and rhododendrons are not known to be hosts of any of those species. The rust needs two hosts to complete its lifecycle, a primary host (juniper or cedar) and a secondary host (rose family: apple, crabapple, hawthorn, quince, pear, serviceberry). You will need to scout your neighborhood for junipers, cedars and plants in the rose family. If you can guarantee that there are no juniper, cedars, or host plants in the rose family within a two-mile radius, then the lifecycle will be disrupted and infection should be minimized. Or, you can remove the serviceberry, which you know is infected and start anew with clean planting stock. For more, refer to the PNW Handbook: https://pnwhandbooks.org/plantdisease/host-disease/serviceberry-amelanchier-spp-rust

Thank you! - Jeff