I am not sure I would do that. He is obviously used to being on his own, and you never know how he would react to the new one, or how the new one would react to him. Too many times they don' t adjust to a new one. Now that you are retired maybe you should just forge the bond between you and him. Just my humble opinion, but I would leave well enough alone.
Cockatiels are very smart, so they have definite preferences in whom they like and whom they don't. Rocky might quite like having a buddy, but you should let him pick his own friend. As in, call whoever you are thinking of getting the new bird from and see if it's OK to bring Rocky along to meet their birds. It will be easier if they have several birds to chose from. Basically, it's birdie speed dating-- in my experience, the hit rate is maybe 1 in 10, but when you get a match, it's so sweet, and they are definitely happier to have a tiel buddy if they naturally like each other.
Bring Rocky with you, take him in a travel cage, and hold it to the side of the new birds cage away from where they are perched. If one of the new birds comes over to Rocky, and if Rocky seems interested, too, you can be pretty sure they'll like each other. If they ignore each other (or hiss at each other), keep looking, or decide to keep Rocky solo. (Just like people: they are happy to be with friends, but would prefer to be alone than forced to be near someone whose presence irritates them.)