Head to the post office. Most major post offices, and even smaller branch offices keep state and federal tax forms on hand. They are usually out in the public area of the post office, but you may have to ask for them at your local branch.
Stop by your town's public library. You can't always find them at your local library, but they are sometimes available at bigger branches.
Look at the DMV the next time you need to handle your car's registration. Most official state and federal forms are available at your nearest Department of Motor Vehicles.
Go to your city's town hall. Again, important federal and state forms are usually available from the registrar or the notary public.
Visit the website of your state's Secretary of State or go to 50states.com (see Resources below). From 50states.com you will find links to the Secretary of State for every state, or the link to the state's Franchise Tax Board. From here you will be able to find a complete list of downloadable tax forms, as well as information as to which form is the one you need.