And pray tell where does one get some "American Elm".? In a 8" round
by 16" size? I would be afraid to ask where I live in the AZ desert.

Good luck - most American elms were wiped out by Dutch elm disease by
the 1970's. There are still a few around, but many of the large
living ones are the ones that are valuable enough to be kept alive by
injections of fungicide, so they probably won't be cut down for wagon
wheels any time soon. Siberian and other Asian elms are not as
susceptible to the disease, so they are more common now, but I don't
know if they have the same interlocking grain characteristics. There
are a few varieties of American elm that have been bred for higher
tolerance of Dutch elm disease, but they haven't been around that
long, so none of those would be large enough for wagon wheels yet.
Sorry this doesn't really answer your question, but I guess I'm trying
to say you might need to search for reclaimed elm lumber, or do some
research to explore alternative woods for wagon wheel hub use.
I'm curious - are you restoring wagon wheels?
Andy