Yeah it does suck and it seems like everyone is against you when noone will help you out, the petshops don't know or don't care what they're doing cant/dont get the drugs and will only sell you stuff they can make money off..
I wish we could get some of the medicines the states can get, alot of them have off the shelf anti-parasitic med's, anti-fluke med's, and even a general cure all that has stuff in it for everything.. Obviously the cure all wouldn't be ideal as your treating for alot of stuff that your fish don't have but it would be better than nothing.. I guess the only problem is that all the active ingredients in these are prescription only med's here so it wont happen
Best advice I can offer you is to have a chat to your vet, I did it when I was already getting our cat seen, if one vet isn't happy to give you stuff then try another and another, I think we have 4-5 vet's working at our local one but the 2 I tried were sweet to give me stuff for fish provided I was asking for harmless stuff..