Michael Denny’s peony bloom date chart lists Dr. John L. Crenshaw as blooming 39 days after Red Charm. It’s got to be a very obscure and hard peony to find, though. Elsa Sass is listed as only 15 days later than Red Charm, and Ann Cousins only 17 days later.
I am growing Lord Cavin (19 days) and Candy Stripe (20 days). They are new in my garden and I know nothing about the fertility of Lord Cavin, but Candy Stripe is recorded as the seed parent of at least one hybrid. Jappensha Ikku is one of my later blooming peonies and has produced seed, and I’m pretty sure it has also pollinated other peonies. It is listed as a “mid season” bloomer but not in my experience. It isn’t on the list. The list is not all that up to date, nor could possibly have every peony. Still, I would recommend checking the list for potential varieties.