Poncirus trifoliata in Canada

I have only visited Canada twice - a couple of days at Niagara Falls and about ten days working in Vancouver in February 2010. The Vancouver visit should have been longer but for an unfortunate stumble which resulted in a severely broken arm and an immediate flight home for surgery!
I believe the climate of coastal British Columbia is mild enough to allow Poncirus trifoliata to thrive. It is hardy down to at least -15C, probably -20C.
In spite of hunting through the botanic gardens at the University of British Columbia, including the japanese Nitobe Memorial Garden, and the VanDusen botanical garden, I found no trace of any Poncirus trifoliata specimens.
However, I was shown one plant in the front garden of a private house in North Vancouver - the owner also having a potted citrus collection with some plants growing outside protected just by a small plastic enclosure. The unprotected Poncirus looked perfectly healthy, although still only a few feet tall.
I have also now come across a photo on the web showing a small tree on the University of British Columbia campus - I must have unknowingly passed within a few minutes walk!