Very nice, all your Chojubai are showing the beginning of the silvery rough bark that makes them unique. Well developed Chojubai, like the one from Don are indeed rare. Young cuttings are moderately common, if you get your reservation in. They sell out fast. I got a young one two years ago by putting my name on a waiting list with Brent at Evergreen. It was only $10, plus $4 for shipping, he listed them in January as being available in June. Sent him a note and money right away. By Feb he listed the June batch as sold out. Got my plant June of 2014. It will be a while before silvery bark forms.
I found that small specimen plants of Chojubai are not as cold tolerant as the large leaf types. There are other excellent dwarf flowering quince that are excellent for bonsai, and are easier to get. Hime and Kan Toyo are my other favorite dwarf flowering quince.