I would just love to have a chicken that comes from a long line of true bred, longstanding, strong and sturdy heritage ancestry, that's all.Namely, the silver grey dorking.
Try the link that Bob posted for Duane Urch. See if he will be offering them this year. He does have SGDs.
You can also join the Dorking Breeder's Club and get a breeder's directory:
http://www.dorkingbreedersclub.webs.com/
The SPPA is a great resource for heritage breeds, maybe not SGDs at this time, but one of the best resources nonetheless.