Lionel had a traditionally sized Southern 4-6-2 that will work with your cars that came with that set. I have one and I can testify that it is a good engine. If you are absolutely wedded to the original engine, you might try shows in your area. The only other way to get that engine is to buy another whole set from a large mail order house advertising in CTT of OGR. That will give you two identical sets of cars, but that would also be a fairly impressive train.