As a manufacture's distributor I thought it time to put in my 2 cents. First, consider all of the known information about "sold" engines. (BTW, Roundhouse can account for every engine sold. In 20 years they have sold collectively less than 3000 engines. An average run is 10-12 engines once or twice a year with the exception of Lady Anne's and Darjeeling's <about 18-20 per run>.) Then consider how many times the same engine changes hands in 4-5 years. Third, consider how many folks have several engines using all different types of fuel. (I personally own engines using: propane, butane mix, alcohol and coal.) Fourth, believe it or not, the distributors listen to the customers and pass that information on to Roundhouse which is why the Forney was built and the SR24 is still built. And last, consider that well over 2000 members belong to the 16 mm clubs in the UK alone. My guess is that there are less than 500-650 live steam enthusiasts (45 mm and less) in the US who actually own and run engines.
Keep your steam up and be of good cheer! Jim Crabb Texas Roundhouse