Darren, Have you looked carefully for an ID tag on the tractor itself? That might give you clue as to the true origin. Companies such as MTD, Gilson, Gibson, Noma etc all made lawn tractors for the "Private Brand" sector. As an example, a chain of hardware stores in three adjoining states could go to one of those companies and have a lawn tractor made with their company name on it and get it painted whatever colour they wanted.
The point is this. There is a vast difference between a company that manufactures tractors under their own name and some department store that decides to dabble in the LT market for one or two years. It may be that you have one of those "orphan" tractors made by one of the above mentioned companies for someone who wanted it called "Green Star".