What Greenlady said is pretty much right. Unfortunately, most
things "parrot" that we know are relatively new. In depth
study and research into parrot illness and disease is much
younger than, for instance, study about dogs, cats, etc.
Therefore it's also constantly changing as the experts learn
more. Things we thought were the gospel in the past can be
wrong by tomorrow, next week, next year. Just my opinion but I
would doubt that Polyoma is the problem. I know it sounds like
the standard response, "you need a good Avian vet" but you
really do. As you have evidently discovered, they can be few
and far between and those of us with birds have to be prepared
to travel further than we would like, to get to one. Just one
of the many down sides to having birds. Here is a link that
might help you locate one.
You can also find local bird clubs by doing a search for them
in your area. Contact them and ask for recommendations as to
who their members use and feel comfortable recommending. If
you are anywhere near a college with a vet school attached,
that is another good source for help. Wish I could be more
helpful and good luck.