Receipt Copy

did you buy it from the Apple online store? If so I found these directions:

you can get copies of receipts for anything ordered through the Apple Store in the past 18 months.

1. Go to the store, clock on Your Account, and log in.
2. Click View Your Orders.
3. Pick the appropriate time from the View Your Orders menu on the right.
4. Click View Order Details on the purchase you are interested in.
5. At the top of the order detail page, click "Login with your Apple ID to make changes to your order."
6. Finally, you'll see a "Print all invoices" link at the top of that page.

where did you buy it from?

depending on how long ago you purchased it, perhaps an Apple store employee could look it up. I would give an Apple store a call.