I am not aware of the import restrictions or need for an import license in China to import from Japan but most import licenses come with all kinds of problems. Since your dad lives in China there are several growers in China that have Japanese origin tree peonies in their stock so you might want to check the Chinese vendors. Most of the ones that I have worked with sell wholesale so I would rather not advise on which ones are best.

If you look through the messages here there was a person that grew cuttings in China that might be able to supply your dad. I will attempt to locate his name but it will have to be in a couple of days. Perhaps your dad would like someone to discuss tree peonies with and this connection could provide that discussion.

Sorry I can not locate the user name of the person I mentioned. Perhaps he will see this or someone will remember his user name.