Still in the making is a directory of nurseries, societies and peony gardens. Takes longer than expected. Those that have grown peonies for a long time will be familiar with most specialized nurseriers, but for those only now getting into the game, it might be interesting to find more information where people can also share their experiences. Below a link to one such nursery: an (older) interview with Binny Plants, in Scotland.
https://www.telegraph.co.uk/gardening/plants/8841625/21st-century-peonies.html