Since selling just the PCB would be pretty weird (you can just order it from @oshpark yourself, and it would be cheaper, considering the shipping), I ordered a whole bunch of those 20mm matrices from the usual sources. Unfortunately, when the package arrived today, I had a bit of a surprise:
I'm holding a 20x20mm, 1.9mm per LED, 788AS matrix. In the box is what came instead: 32x32mm, 3mm per LED, 1088AS matrices. I'm pretty sure that is a mistake on their part, since those matrices are much more expensive, but it's still very annoying.
Now I have several options. I can negotiate with the seller, and maybe they will replace them — then I'm back to my original plan. I can make a bigger version of the matrix sanitizer and sell that — but those bigger matrices don't fit the breadboards as well as the small ones do. Or I could come up with some other project that utilizes those matrices, possibly a lot of them all at once. For now I let the seller know and we will see where that goes.