We were at Colonial Williamsburg last week...they have a nice sized flock of single comb Nankins, but have only a trio of rose comb Nankins at present, as the normal place they keep their Rosecomb Nankins is being "fixed" to keep out a mouse infestation.
However, most of the birds in the United States have originated from the Colonial Williamsburg Stock, one way or another. If you trace the history of the breed, you will find this to be true. They got their birds from the author of the book "The Nankin Bantam," who no longer has birds. Elaine Shirley, the coordinator of CW's Rare Breeds program, has been spreading Nankins around slowly to various flocks for many years...and those folks have spread theirs on to other people.
I'm beginning to see some great differentiation between birds raised by different breeders, now that the CW birds have been "out on the market" for quite a number of years. Most people that have gotten them have gotten them in about the last 10 to 13 years. And most of THAT subset has gotten them in the past 4 years or less, with the exception of a few of the earlier pioneer breeders that started that Nankin Club of America in 2006. Prior to that, VERY few people had them.
Our birds come from a variety of sources...some from Monte Bowen in Kansas (who got them from CW,) some from Don Cable's line (who got them from Monte Bowen, then did some significant breeding), some from another breeder that no longer has birds due to his health.
Most "adult" breeders here in California no longer have birds, or many of them. For the most part, it's 4H kids that have Nankins now in this area (Northern and Central California). There are, however, some very nice quality birds in these small flocks, the result of several years' intensive breeding by various people.