For any who might be interested, the first four volumes of the Koza are up for auction on the Yahoo.jp auction site.
The seller provides pictures through the link, and describes their condition as what we would call "lightly used", with yellowing of the paper
and impact damage to the cardboard slipcovers.
Early bidding is pretty brisk, with the latest bid at 10,500¥.
Due to the weight of these books, insured shipping will be very expensive if you are outside Japan.
Auction ending February 19