This is fascinating. From a web search, the American Chestnut Foundation has a formal process for submitting a sample.
On their request for samples, and why [0]: "Please let us know if you think you have found an American chestnut by submitting a Tree Locator Form and leaf sample. We are always looking to expand our inventory of chestnut trees across the native range. [...] "TACF is continuing its breeding program to make further gains in disease resistance and forest competitiveness, as well as forest health and restoration in general."
On how to submit a sample [1]: The foundation has developed a procedure where you can submit a twig, leaf, and photos to one of their representatives, to verify if the samples came from an American chestnut tree.
Every survivor is another set of genes that maybe lead to the revival of the species.