I wrote to Esther Simmons a while back to get a price list for the upcoming season. Got a reply from her yesterday and it was not good news for us—they've decided to retire from selling tree peonies. She said that shipping overseas last year was a nightmare for them—every country, not just the US, and they're just not up for it anymore. There has been rumor of them retiring for a few years now so it's not a total surprise but it hurts to lose a source as wonderful as they've been.
If anyone is interested in seeing their email response I'll certainly take a screen snap and share, just let me know. They did say they would continue to sell a herbaceous hybrid they developed and might eventually sell their breeding stock but I doubt if that would be shipped overseas.