rocksnstumps
5 year old buck +
Don't know if this has been referenced before but this guy has compiled quite the list of sources and makes mention of cold hardiness in his other links about rootstocks. Too much info for me, I just plant what I can get from local sources, but others may be interested.
Link
http://www.appleman.ca/korchard/supplies.htm
Link
http://www.appleman.ca/korchard/supplies.htm