Dirr says: "...there are many cultivars of this tree but two which are well adapted to cold conditions are 'Carpathian' which was brought to Canada from the mountains of Poland and supposedly bears heavy crops even when temperatures reach -40°F, and; 'Hansen', an annual bearer, shells are very thick, easily shelled and the nut meats are classed as excellent..."
hortster

Carpathian is probably the name you were looking for. Note that "The term Carpathian walnut is now applied generally to all cold-hardy J. regia in North America, whether from Crath or other sources" (A.L. Jacobson, NORTH AMERICAN LANDSCAPE TREES (1996, Ten Speed Press, Berkeley).