Hi Boonta,
Only problem I see with this is that anything you make will be one off's. I can't see anything worth the expense being made for the push mower market. The ride on market is where people have to spend money to keep them going but there is nothing I can think of that could be made in multiples, everything is going to be an individual item, and then you have the other issue that everyone here is hunting for the cheapest way to get their machine going again.
Anyway good luck with the idea but as I have said here many times this is for me a cost neutral hobby that I would struggle to make beer money from
