@shinmai - next time I see you remind me to tell you about ''hanging out'' with the plant taxonomist that was mapping distribution of Dalbergia through the forest of a country I won't name here.
I am skeptical about a complete ban on importing 'Chojubai' or Chaenomeles in general from Japan. I believe there is a quarantine requirement, but I don't believe there is a complete ban. For fruit trees, which would include Chaenomeles, I believe the quarantine is a full 2 years on the USA receiving end. There are likely no shortcuts, with azalea the quarantine can be "served" at an inspected and approved nursery in Japan and therefore shorten or skip the quarantine in USA after import. But I believe no matter what a Chaenomeles imported would require 2 years after arriving at the USA Port of Entry (Miami is the best port to use for plants). I could be wrong, but I believe this is the case. The quarantine requirement adds hundreds of dollars cost to importing a plant and the arrangements made are complicated and detailed.
However, Chaenomeles, flowering quince, including 'Chojubai' are already in the USA in fairly high numbers. Just about everyone in bonsai I know, that has been around for more than 5 years has a 'Chojubai'. They root from cuttings easily. There is no reason for them to be considered ''rare'', except as hype to drive up prices.
Now it does take 30 or more years to develop an 'Chojubai' old enough to have the unique silvery bark that they are famous for. I can see paying significant money for a well developed 'Chojubai' that has nice rough silvery bark. I see no point in paying more than $100 for a young, 'Chojubai' with no age or size to it. It it isn't old enough to have the mature bark, it isn't worth more than a similar size of any other cultivar of Chaenomeles.