I'm glad you are willing to take the time an effort to keep Bobo out of a bad situation. It is terrible when they are shuffled back and forth between owners and pet stores. What a miserable life that would be, especially for a bird who was yanked out of his natural environment. It sounds like you are making progress and that's great! Do you whistle back? One of Timber's favorite things is to whistle back and forth with me. That is a natural form of communication for them. Sometimes he will mimic what I whistle, other times he does his own thing. You've probably noticed that your grey whistles a certain pattern in the mornings? If I understand correctly, that is their natural flock "call." He's letting you know his location and leading you too him.
One thing I wanted to mention, though you may already know. A parrot is never "tame." Bobo will never be domesticated like a cat or dog. He will become attached to you with time, and you will be able to teach him things like stepping up etc., but he'll never be tame. Even parrots who are bred and born in captivity aren't considered to be domesticated. Remember when you get to the point of handling Bobo (it may be a long way down the road) that parrots are prey animals in the wild. Trust is hard to build, and they often react out of fear.