Ffestiniog Railway's Boston Lodge Engineering Works has an online brochure that depicts several impressive examples of the firm's car-building prowess -- including a set of exterior and interior photos of that SR&RL parlor car. The brochure points out that, "aside from the carriage works (i.e. car shop) we also maintain and build locomotives." I have no doubt they could replicate a WW&F locomotive - but I also suspect it would be pricey. By the way, the brochure is at:
www.festrail.co.uk/publications.htm?mm=7