What you can do right now, while sourcing OTC:
1. do what you can to prevent spread by either giving each hive their own hive tool (which never visits other hives), or heating up the hive tool in your pumped up smoker between hives.
2. beekeep with bare hands and wash in soapy, bleachy water between hives.
3. do not put frames or stores from one hive into another
4. arrange the hive entrances so they are as far from each other as possible and point different ways (reduces drift, which is very common within any group of hives) and/or put on robbing screens to discourage drift
5. disinfect ALL your spare equipment, ditch all extra frames of stores you have on hand to give back to the bees (since you cannot be sure they are not contaminated)
6. feed syrup and protein patties (feeding helps the sick larvae survive), consider acidfiying with lactic acid as that seems to help as well.
7. get an experienced beekeeper over to check the hives with you, preferably a member of a local club who has experience with the foulbroods.
And....if this foulbrood is in one hive only, consider euthanasia to shut down spread. You can kill a hive quickly and humanely with a big bottle of rubbing alcohol poured down the seams AT NIGHT WHEN ALL THE FORAGERS ARE HOME! Close up entrances before application, seal the hive, bag it and take it away next day for cleaning and disinfection.
Then, once you get the OTC, dose all the hives in the apiary as when one has foulbrood, the counts of the pathogen skyrocket in nearby hives. It is not just one hive that is sick, but the whole apiary.
One reason to buy local bees (usually nucs in May or later) is that you can inspect the bees before purchase and you are not bringing new/more diseases or pests into your area. In our club we are trying to all keep an extra colony or two in all beeyards to supply local demand for bees.
Somewhere online one of the bee supply places has a protocol for getting prescribed OTC. Will post it when I find it again.