It is by prescription only so legally in the US you must purchase from a Veterinarian or a doctor of Medicine that can write scripts. Some LFS do sell this if they are willing to take a chance, but legally it's from the Veterinarian. Hope this helps and if you belong to a local reef club someone might give you some for a few of those pretty Zoas :D.
You need to go you YOUR vet if you have other animals that you take. The reason is they will be much more likely to listen to you and to help you because you are already a customer of theirs. If your reef is your only pet it can get hard because they would rather not mess with it because them writing you a script or even selling you the meds is not very profitable for them.
Wherever you end up, take in a copy of dustins treatment plan and also you could take pic to show the vet and explain that its similar to your dog having fleas. they are a parasite and they host on the coral, make sure you let them know that they are damaging your animals health.
Kevin ,
I Just got refer from one of local reefer here , and I'm in contact with the person who may be able to spare me some,I will post update with out come.
Thank you for your quick response.
Ben