You could try these guys, If they haven't got any, they might be able to get some. They were very good. I missed them dreadfully when I moved 7 yrs ago. But I transported over 200 plants I'd got from them, when I moved, as I brought alot of my garden with me...

http://www.acorn-mk-nurseries.co.uk/index.htm

google garden centres and the area you live in (ie county) and that should help , and the only other thing is , i know its a pain but you might have to make a few phone calls

Thanks - but I gave in to temptaion and bought the mail order tubers. They haven't shown any growth since potting them in March, so have emailed the suppliers!