Most tractors of the period were unsprung, the front axle was pivoted in the centre to keep all four wheels on the ground in rough country. Universal Hobbies produce a Fordson Major tractor attached to a key ring! In fact it is so close to the Oxford model in detail and scale I at first took it to be the same casting. The most important difference is that it doesn't have the shiny front axle, the front wheels are held in by two plastic pins. The other difference is that it only has a rudimentry exhaust stack and the attachment for the keyring which is a tab with a hole where the drawgear would be. It might be possible to modify the tab to represent the drawgear. There are 3 other tractors in the range, a grey Fergie and a later M-F that are overscale for 00 and an un-named tractor that looks like a mid 50's Massey-Harris with grey instead of yellow wheels that also looks very close to 1:76 scale.
EDIT Arthur just beat me to it re. tractor springing, or lack of it. The Universal Hobbies models mentioned above can be found on E-bay. They produce models of more modern tractors in smaller scales as well as other farming machinery some of which can be used with 00 models without being too obvious.