Ken,
Check my pervious posting, and click on the link to the Strasburg RR web site. They now manufacture brand new replica Sellers Type N horizontal lifting injectors.
However, the work Gordon is doing is beautiful and I have no doubts that the injector he is working on will work properly once the small finishing details are attended to and that spare injector is in service.
There are also supplers in the United Kingdom that manufacture new injectors, although they are of the Gresham and Craven design and will have British Whitworth threads, requiring an adaptor to connect to U.S. pipe fittings.
They would not be an authentic accessory for use on an American narrow gauge locomotive.
Keith