Howdy Hal
AMT/ERTL made a JOHN DEERE 4430 plastic kit in 1:25 scale, last produced in 2002. You can usually find them on Ebay. Highway Miniatures used to produce some 1/87 (HO train scale) FORDSON tractors, a good hobby shop may stock them. As to anything else being produced in kit form I'm not familiar with. There are however a ton of 1:16 scale built up diecast(and some resin) farm tractors, both wheeled and tracked. You didn't mention where you hail from but if you are near a place that sells farming equipment, they usually stock John Deere, Case, International Havester, etc "toys" as part of their inventory. As to the "toy" part, the ERTL fine scale collector series are a thing of beauty, the detail is such they are beyond the "TOY" catagory. Good luck in your search.
Mike