This probably a long shot, but worth a try. Is there anyone selling "treatment-free" bees in Canada? In Ontario would be ideal. I know that there are organized breeding programs for mite resistance. The Ontario Beekeepers Association has one for example:

http://www.ontariobee.com/index.php?...ay&cat=53&v=74

I am not having a lot of luck finding a source that doesn't treat at all.