Collect copper wire from your friend's, your parents' or your hardware drawer or work room. If your project doesn't depend on having pure copper -- for example, to observe the effect of acid corrosion -- then you need not purchase copper at all.
Visit your local hardware store and purchase copper pipes. You can use copper pipes for the same purpose you would copper wire, but given their size, you can use them in larger-scale experiments. Consult with the hardware associate at the store to locate piping made of 100% copper if purity is a necessity.
Peruse the database on the Copper Development Association website, linked under "Resources" for a retail copper supplier near you. Scroll down to the bottom of the screen, select your state from the menu on the right and click "Click Here to Search."
Speak with your teacher and have him order copper from a scientific supply company if you need a special form of it -- for example copper chloride (CuCl2) powder. Depending on where you live, you might not be able to find chemical compounds containing copper at retail storefronts, so your instructor will need to obtain this for you.