The reality of it is, that if you want the best for this horse, there are 2 options in which you will know FOR SURE what has happened to him. 1) you keep him 2) you put him down
Now 2 would be the 'worst case scenario', but when you are looking at behavioral issues like his, and with the stipulations YOU are personally looking for, the chances of finding someone who is willing to take on an animal like this for life, is a long shot. There are people who have the skills the train or retrain a horse like him, but they may not be looking for a life time horse, but a project that they train, and resell.
He is unfortunately not gentle enough to wind up into organizations that would actually take him for life, with the stipulations you are looking for (these being programs that help the disabled, and other such programs that need gentle well broke horses). I donated a horse many years back to a program that helped disabled people, but he was broke to the nines...I rode that horse without a bridle.
I think you need to really think about what you are asking, and what the reality of the horse economy is. I think you need to find someone who has the ability to retrain him, and if they wish to resell later on, you NEED to be willing to accept that...he will not be yours anymore, once he leaves your farm. Or, you need to just keep him, and keep working with him; perhaps try and get into a good clinic with a good trainer...sometimes that is what horse and owner need, and sometimes you can get in for free, if the trainer can use him as a demo horse.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."