So what exactly makes these valuable?
I'd guess the dragon is what does it. They certainly aren't rare, as I see them for sale often enough online. There are some other notes issued by the Japanese Occupation of China that have a dragon on them that are much much less expensive, and you may want to look at China Military notes under the Japanese Occupation rather than the China Puppet Banks to find a cheaper dragon note. Those that you have, however, always seem to carry a premium. When perusing online, you may find one the seller hasn't researched enough. Some of these style notes I've got from the 'junk box' at coin dealers... I rarely go to a coin shop though, so it's been a while.