These Japanese prototype cars were some of Con-Cor's first N scale imports ever and actually predate any of their North American prototype models. They were manufactured by Sekisui Kinzoku (Kato's ancestor). My guess is that they were a fairly short-lived offering as they seem to be pretty scarce these days. The observation car was included as part of Conrail's "Inspection Train" boxed set.
Combine -
Coach -
Diner -
Observation -