@RichardW Looking into this, it seems you could just create gift cards manually in Shopify (without associating a customer), and then copy and paste those codes into an excel spreadsheet to send to a manufacturer to make them. Some things to keep in mind:
After you create the gift card, you cannot see the code on the gift card itself, or export the gift card code out in bulk. So, you’ll only be able to view the code when you create it (which at that point you’ll want to copy over to a spreadsheet for storing it internally).
Hope this helps!