I have one suggestion. He might want to talk to Bill MacKentley of St.
Lawrence Nurseries.
http://www.sln.potsdam.ny.us/
Have him first look over the Nut Trees link on the opening page. Note
that he only sells seed grown trees, not grafted. (He might be
interested in buying a supply of nuts from your friend's tree to produce
seedlings. Maybe, maybe not.)
Bill loves to talk about hardier than normal fruits and nuts. I bet in a
few minutes of discussion he could form an opinion on whether the tree
is really something special, or not.
There is an e-mail address on the web site but I have had no luck
getting him to answer e-mails, and he KNOWS me. (Maybe that is the
problem? LOL) I suggest trying the phone number. Long distance is cheap
these days and it would be well worth it.

Steve in the Adirondacks (Tupper Lake, in fact, and about an hour away
from Bill MacKentley's place)

simy1 wrote:
A friend knows of a walnut growing in the central northern MI
peninsula (he has known that tree for a long time, it's just that
suddenly the light went on in his head). It produces good nuts and it
is in his property. The interest is, of course, that the tree is one
zone colder than its typical northernmost range (at least. it is a
place that has experienced a killing frost every month of the year
since records were taken, low Zone 4). He is interested in talking to
people about propagating it and possibly making it a named variety.
Any suggestions?