Saint John of San Francisco concelebrated with and communed New Calendarists from the Greek Archdiocese. He did this all the way up until his death.
I won't mention Fr. Seraphim Rose because this site seems to be 50/50 on whether or not he was a saint.
Metropolitan Saint Anthony Khrapovitsky with his cell attendant and EP Bishop in an Anglican procession, Britain, 1925. In celebration of the anniversary of the First Ecumenical Council
My point being that the ROCOR wasn't as walled off from World Orthodoxy as some people claim.