Hi,
Hope this not too late and you come back to read this...
I work on a horse stud and we often have overseas staff working for us. They usually find the job through a job agency which also helps them with their visa's etc...
The farm also sponsors many of these people to stay here in Australia.
So to answer your question ( I hope), If you want to work here, you have to have a job and then apply for the visa. You can't do it the other way around. But, sorry, I don't know of any vet practices that would be able to help you in this way.
Good Luck in your search.