The arboretum is listed as between zone 5 and zone 4, so while cold it is not excessively cold. Like coastal British Colombia it get a maritime buffer effect.
http://www.nuttrees.com/edible-nut-trees/other-edible-nut-trees
This Canadian Nursery has quite a few Walnuts, Pecan, Heartnut, Hickory and Chestnut that is rated for zone 4 and Hazelnut that is rated for zone 2. So there is quite a few options available for folks on this side of the
pond. But I am supper happy that folks on the other side of the
pond have resources available to them.
Iterations are fine, we don't have to be perfect
My 2nd Location:Florida HardinessZone:10 AHS:10 GDD:8500 Rainfall:2in/mth winter, 8in/mth summer, Soil:Sand pH8 Flat