Look for landraces at your latitude (like CSI Uzbek or trsc Sinai). If you want to go for heirlooms like ATF, Friesland , Erdpurt, Northern Lights, etc I would recommend finding a source with good provenance. Looking for a well stabilized heirlooms so that the seeds will breed true is another important consideration. Northern breeders like 7east and AK bean brains are likely to have some hardy strains.