You can buy a crochet afghan chart from the site below. You can see a picture of it near the bottom of the page. It's even called a Farmall tractor!

Here is a link that might be useful: Project Linus

Oh my goodness, you have no idea how you have helped me.......thank you so much......I have been searching and searching for days......my friend mentioned it today and decided that since I have made him numerous afghans that maybe I wouldn't mind making a tractor afghan for his 11 yr old nephew who is just as obsessed with them as he is...you are going to make one little boy and one uncle very happy....thank you so much!!!

Joanne