I'm sure that you'll be able to find a sheep farmer or friendly veterinarian that will supply you with some veterinary ivermectin – it’s used primarily as a sheep wormer. It’s is not water soluble and is dissolved in olive oil and applied topically. Your vet will help you dilute it and show you how to apply it. Be careful to keep it no more than a few weeks as I have had old stock kill Gouldians. I’m not sure if the chemistry or concentration changes but it becomes toxic.