This might be a possible alternative. I managed to find a 1961 issue of Model Railway Enthusiast that has a feature on building a CEP by modifying Kitmaster Mk1 coaches, which you can still find in some places. Requires dishing out a lot of Plastikard and cutting and painting, that's if you are willing to paint the NSE colours and have a lot of time on your hands. The end product probably won't give you an accurate model, but rather a representation of one.