You might look for a pattern put out by "EweCANknit." It's pattern number 1801, "the tractor"

I found a link for you to try:
http://www.generalbaileyfarm.com/patterns.htm#Ewe%20Can%20Knit%20Knitting%20Patterns

It's so easy to make your own pattern!...
Use a plain pattern for a sweater you like and draw the sweater out on graph paper.....then draw on the tractor or whatever. Coloring books have simple pictures you can use as a pattern if you can't draw....then, mark the different colors and knit your sweater following the graph.
I have done it with chicks, ducks, kitties marching around the bottom, lambs jumping over a fence, a row of tulips, snow flakes, santas, reindeer, beer mugs, christmas trees and about anything else you can think of...
It's easy.....and completely your own!
Linda C