Buy one from a breeder. That's my first suggestion, but since you are beyond that. it sounds like you are making progress. YOU HAVE TO GAIN A BIRD TRUST, this can take weeks, months and even years. This is why I would never recommend a rescue bird for a first time bird owner.
It will take a lot of patiences..........oh did I mention that IT WILL TAKE A LOT OF PATIENCE. The best way to gain their trust is by sitting near their cage, talking to them, singing to them reading to them and offering them treats from your hands. YOU WILL GET BIT and most likely numerous times. But that is one of the drawbacks of owning a bird. If he is flighted, have his wings clipped so that he is soley dependant on you. The worsest mistake new owners make is once bitten, they steer clear of the bird leaving it locked up in it's cage, which only further desocializes the bird. Then after several months or years, they list it for sale or drop it off at a rescue center. Please don't be one of these people. Take the time and interact with him, I think he will eventually come around.