Because the charities are acting in the interest of the animal welfare, not profit, they desex, vaccinate, and test for diseases. They usually have processes to get to know the temperament of the dogs, too, and can help find a good match.
There are many dogs in need in Hong Kong. Many are killed each year because there aren't enough homes. So it's strange to be breeding dogs at the same time to sell. The breeders also tend to dump puppies and the breeding dogs as soon as there's a health problem, even if it can be treated. Leaving the charities paying for their mess.
Try approaching a few charities and see which is easiest to work with. You may need to wait but usually a breed will come up for adoption.
Will post a list when at a computer, but I think there's a list pinned on this forum.