There is no requirement that you have an original sales receipt, but there is a requirement that you and your personal injury lawyer must prove a sale occurred. This can be proven in many ways besides having a sales receipt.
First, you may have some other evidence like a credit card receipt, or the original product packaging, or some other evidence that verifies the purchase. Also, the law doesn't even require that you be the purchaser, like in situations where you get a new product by gift or by simply being near the dangerous product when you are injured.
Also, in medical device transactions, like where a device is implanted through surgery, you won't likely ever have a sales receipt.
So the bottom line is a sales receipt is not required but corroboration is necessary to prove the transaction or sale did occur. As well as evidence showing the product type, make, and model is critical. Never return that evidence to a manufacturer or distributor without first consulting a personal injury lawyer about the claim.