Malcolm, I could be wrong but I think the one sold by Maxitrak could be a model of a LNER C53 which is a 0-6-0 steam tram. I,m guessing it was scratch built but there could be plans I dont know..?
If no full plans you could always look for 0-6-0 chassis plans and then scratch the body which is not complicated. The 08 diesel shunter chassis for electric models (or other 0-6-0) would do the job but again I dont know if there are plans for them.