Receipt replacements.

Have you checked your purchase history at the online Apple store? Or contacted the physical store where you bought them? Or, third possibility: pull up your warranty info via online support and your Apple ID and then contact Apple referencing that info?

If/when you get them, you may want to consider scanning them and parking them in a folder in your documents folder - I've been doing that for years for any purchase over $100 or so (or any that has a warranty and may require service). It came in handy recently when they wanted a copy of the receipt of a $700 appliance before replacing it.

Go to the store where you bought those devices and ask.

Well, that still leaves the other two possibilities.