Hi Scott, it's not so complicated, if a treatment has been aproved for fish (MS-222 for exp) the vet won't be allowed to give or to use an other one wich is not aproved (benzocaïne) BUT if no treatment at all has been aproved for a specific pathology, the vet will be allowed to use a product that he think suitable ,as soon as the animal won't be eaten.
I don't know what will be the solution for most of the hobbist, maybe some koïclub could have a vet between the members that will find a local solution.
I agree that most of vet doesn't know a lot about koi pathology, but I suppose a lot of them will be interested to find discover something new (i meen only interest, not money). Maybe they will know a little more about drugs then the guy who take care of a petshop or who sell the drugs at the moment.
Any way that could also stop some people to use drugs like salt and peper in a kitchen, without knowing their toxicity.
IMHO the solution could be in the koïclub organisation.
Marco