You can usually find a copy in your past orders section on your Amazon account:
To print or download your invoice or order summary from Your Account:
1. Go to Your Orders.
2. Find the order for which you need to print or download your invoice or order summary.
Tip: If you don’t see the order you’re looking for, select another option from the Orders placed in menu.
3. Click on Invoice.
4. Depending on which Seller you placed your order with, you can do one of the following:
If you placed an order with Amazon, you should be able to print an invoice for your order and you will see an option to Print Invoice. You will also be able to print an Order Summary.
If you placed an order with a Marketplace Seller, an invoice will not be available for your order and you’ll only be able to print the Order Summary.
5. You can now print your invoice and/or order summary.