I've ordered parts direct from Freightliner Custom Chassis (FCCC, not Freightliner truck) and paid with a credit card over the phone. They probably don't stock parts that are no longer used in current production, though. A phone call to their Help line (1-800-FTL-HELP) should get you a part number and maybe the supplier name, though. Have the last 6 of the VIN handy when you call.
However, I'm not sure the dash light switch came from Freightliner at all. Mine did not - the coach builder put the dash together, with some components from FCCC (e.g. ignition switch & air brake knob) and the rest their own stuff. Tiffin may be more help to you than FCCC.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC