Programs don't tend to take donated dogs. Instead of trying to get a placement for this dog in a service program, you need to find him a good home. His odds are very slim at making it on the SD road while, with his therapy backgraound, his odds of succeeding in a family home would be excellent.
Many programs are breeding their own dogs because it significantly increases their success rates. They are able to control a large number of genetic factors and make solid predictions on how well a dog will hold up physically over a working life. It is not practical to put two years of training into a dog to become a service dog just to have him have to retire after one year of work due to a health problem.
Paws with a Cause did a study of 10 years of their intakes which they selected from shelters. The net result of this study was that fewer than one dog in a hundred was able to meet their initial requirements for temperament and health and actually complete training to be placed as a service dog. When they switched to breeding in house, their success rate among the dogs they produced themselves rose to seven successes in eight. That's more than a significant improvement.
Of those programs that do use rescues, they have their sources picked out. They choose those sources that consistently produce the sorts of dogs they are looking for. When you deal with "Joe" from Acme Rescue, whom you've known for years and you trust Joe's ability to evaluate dogs, and he recommends one, you've probably got a keeper. But when you deal with "Tom," a total stranger, from an organization you've never heard of, or from no organization at all, you have no way of knowing what you are dealing with and whether they are competent.
Lots and lots of rescues find a nice dog and think that a service placement would be just perfect because this dog needs a home and some disabled person needs a helper. But it just plain isn't that simple. The vast majority of these dogs that rescuers, knowing nothing whatever about service dog selection and training, think are ideal, are not suitable. They look at a dog who is sweet and affectionate, and I, as a service dog trainer am looking for one who is a bit hyper, a bit aloof, a bit destructive.... I don't need sweet in a service dog, I need determined, a bit stubborn even. I don't need a dog who will comfort the handler who can't get the door open, I need a dog who won't give up until he gets that door open.
While some people with service dogs do also volunteer as pet therapy partners, all that the two groups of dogs really share in common is good socialization and manners. I can take any nice pet dog with good manners and temperament and turn it into a therapy dog in 8 weeks. If I take the same dog and try to turn it into a service dog, I'm almost certain to fail and it will take me 18-24 months to prove it.
So the best thing you can do for your dog is focus on finding a good pet home. There are plenty of people I've noticed lately expressing an interest in doing therapy dog volunteering and asking questions about what kind of dog to get. So there is a market for the specific kind of dog you have, rather than trying to put him onto a career path that probably isn't going to be a good fit.
In short, his odds of finding a good pet home are significantly higher than his odds of finding a placement as a service dog. So that's where you should focus your efforts.