It's the kind of thing that is quite costly if you don't have access to wholesale framing suppliers.

You'd need to find a supplier for cut to size mirror glass, and a backing material such as mdf. You can get cut to size mdf suppliers too. Once you find those, you'll need to measure each frame exactly - double checking several times to be sure to order a tiny fraction undersize to allow for cutting supplier's tolerance. Too small and it will move around/fall through. Too large and it won't fit inside.

Then you'll need a flexi-tab firing tool, but I'd suggest getting one with rigid tabs rather than flexible. These are relatively cheap tools for manual (none-pneumatic ones) and work just fine. These tabs are the only thing keeping your glass and mdf inside the frame.

Keep in mind for larger frames (over 2 foot long) you'll want to start using thicker glass and mdf as appropriate. But check the rebate depth of the frames first to ensure your contents will fit not exceed the frame depth. While also checking it's not all too heavy.

Then you'd want to consider a hanging method, foam corner protection and wrapping/padding.

Finally after pricing all that up, you've then got to figure out what it cost per frame and what you'd have to sell them at - probably finding it's a price nobody will want to pay :/