Thank you, I appreciate your kind words! And yes, I did have a feeling that my question might be a little impossible. According to Google, the only elms in Canada that are positively known to be without disease are the ones in Alberta and Vancouver. I'm not sure if I could narrow down what suppliers use them, but maybe. The Oregon Harvest responded to my email saying they asked their quality control and their supplier and both denied contamination, and also said that the inner bark can be harvested from diseased trees, they just use the parts that aren't affected yet. Makes sense to me! I'm guessing a lab test wouldn't show anything either way and with the answer I got from them I may be being too cautious to not buy something from them at this point, so that's what I think I will do. Thank you!