I'm not sure that Sierra still make this switch any more I could not find it or a replacement. Most Sierra switches are now used by the marine industry. Ask at you local marina or boat parts house. Cooper lighting makes switches similar in looks to your switch, but they are not the momentary contact type. There are toggle switches that do what your switches do, but probably want mount correctly. You may want to replace the light fixtures and probably the wiring if wired for low voltage, which from your pictures looks like the case.
This is a pic of a Cooper switch available at most home stores.