20th Century Rider
Engineer
Pacific Parlour Car came pretty close to checking that box.
Yes it does... but does that define it as a speciality restaurant?... what would be the definition of what a speciality restaurant would be on an Amtrak train? And just what is the speciality food that was served? Was it regional? Was it some kind of ethnic or ethnic mix? The parlour car served meals which were probably a step above what was served in the dining car... perhaps 'California Cuisine... but does that make it a speciality restaurant of Cali Cuisine speciality food? Maybe it does.
Here is a fun take on what 'speciality restaurant' on a traveling train might mean... but even this doesn't seem to answer the question???...
https://jamarattigan.com/2019/04/12/all-aboard-for-the-dining-car/