Oscar (fruitlovers) could probably help you find that as he is based in Hawaii? If not, my favourite people to bother for any European and North American plant is Royal Botanic Gardens in Kew - they might not have a living specimen but they are usually good at digging up who can help you find what you are looking for or where a live plant specimen could be found (I think it only means they are better at badgering other countries' Botanic Gardens staff or they just better used to dealing with inquisitive gardeners).
My past enquiries were mostly about ornamentals (cycads, various epiphytes and vines) but I think they try to help with any plant related question. Give them as.much info on the plant you are after I've noticed they get back to you quicker that way. info@kew.org is the main email address but a specific staff will get back to you depending on the type of plant you are after.