Go online to your local library website, or down to the library itself and ask for books on plant physiology. Inside these books you will find several diagrams, and you can simply copy them and take them home.
Calling up a local school, high schools or colleges will be your best bet. Ask for the science department, and when someone picks up, give them your name, what information you need, and whether they would be willing to help you out. Most schools will give you a diagram of a leaf.
Go to your local bookstore. Look in the textbook section for books on plant physiology. Look through and find the book with the diagram you would prefer, buy it, and then take it home to use as desired.
Go online to a reputable auction site, wholesale site or outlet site, and search for plant physiology. Some of these sites allow you to look inside the book to make sure you're getting what you want, and you can normally even read the first couple of pages.
Go to your nearest college bookstore and buy any textbook on plant physiology. You can look through them to make sure they have the pictures or drawings you want before buying them.
Search online through a search engine for leaf structure drawing, or leaf diagrams. This will bring up several results. Search through, find the diagram you want and print it out.