Maybe these guys, but I'm hoping for something much better, although its not much hope either lol. Too burned by how CP0 turned out to be fodder.
I was thinking these knights might be inspired by the Knights of Arthur, Knights of the Round Table, all that Camelot stuff and such. Lady of the Lake, Excalibur Merlin, Lancelot etc.
There is also the Holy Grail which is believed to provide immortality too. Oda might reference that in OP like with the Ope Ope no mi supposedly being able to grant eternal youth/immortality or whatever or even the national treasure of the holy land/Mary Geoise, whatever that is too.