Hi Brian
Roden do a 1914 pattern RR armoured car and a Holt 75 tractor in 1/35 but in truth there is not much out there from the mainstream manufacturers. There are/were some nice resin offerings from the cottage industries but these are formidably expensive - which is fine if this is an area of real interest to you, but if, like me, you just want an occasional vehicle or cart etc as background for an aircraft model, 100GBP+ might be more than you wish to lay out.
I tend to buy old Airfix model T's etc and hack them about with much added plastic card to get something suitable.
Sandy