My ecclesiology professor assures me that there are religious permanent deacons, but I have never actually met one. I would assume it is for similar reasons that you rarely see a secular deacon that is not married or a widower. In the case or a religious perhaps they simply feel their religious vocation serves similar needs as the diaconate?
I have no proof (having never met one), but I would suspect that this would only be in active orders like the Franciscans. Iād have to think of how a permanent deacon would live out their ministry in a cloistered/contemplative order. That being said, it is always possible that a friar that was on the path to priesthood might stop after being ordained to the diaconate. While we often treat a transitional and permanent deacon as related, but different beasts, they are no different from a sacramental standpoint.