Well first they are not a member of Paeonia japonica but are lactifloras. Little information on Ok-na-nami other than it apparently exists. Clairette according to Carsten's website is a single. One reference states it is straggly. Always try his website for information as it is one of the best in the world.
What kind of peonies are you looking for tree or herbaceous? Is there a website for the garden? There are various groups doing similar things. If there are many peonies Boyd's 1928 book could be of use. One thing to check is for nurseries that used to be in the area of the garden.
Local nurseries were searched first, but to no avail. There arent any that were in business back then. Many of her plants came from upstate NY nurseries anyway. Ms. Shipman's notes and records are incomplete and some are illegible about this particular garden done in Toledo, Ohio in 1938 towards the end of her career. Cornell University has all of her materials that were saved. She didn't save much. It seems that the notation "Jap" peony is not correct. I've found all the peonies called "Jap" as herbaceous. Oddly, every single one was a pink.