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.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL