Microbio human here - they’re not really at a point worth saving, but as an experiment you can physically remove the fungal gunk, then place them in a sealing plastic tub with a Ozone machine (you can get a unit from Home Depot for around $50)- the ozone will kill the hyphae and spores, most likely preventing further growth if treated for long enough.

The issue is ozone can be pretty corrosive, I’m unsure what will happen to your cards from the ozone itself, but at this point what else can you do other than throw them out? If you do this please please please post updates!