I've been scouring the Web looking for parts or sub assemblies as well. It's a sort of closed shop, methinks. I would have liked to save the price of the trailer by building my own. All I wanted was the axle and rear wheel assembly.
but these are not available separately.
I watched the film and thought your tractor looked cute. Carson seem to do the right scale but they are Ready to Run types.
Here is the best site for prices, as recommended by the Tamiya GB club that I've joined.
and here is my latest club.
My Wife saw the prices last night and there now may be a doubt until I sell some of my boats. (quote)