Citrus, Rangpur Lime, Mandarin Lime, Tahitian Orange 'Otaheite'

In Palo Alto, California an established Rangpur Lime produced three crops a year of orange extremely tart fruit that made a fabulous "lem...Read Moreonade". It took no care at all (aside from being careful of those thorns!) and is the most cold-hardy citrus known. When I moved north I started some plants from seeds that grew for a couple of years through some snowy winters, but in the midst of family crises they were neglected and died before I could grow them to fruit-bearing. I'd love to get some more seeds, or a plant to try again in this colder zone.