Have you tried Colt's custom shop. They used to do it and mine is the sweetest double action pull I've ever shot but this is on an older pistol. Little pricey, but what the hell. Its a job you don't want anyone to tackle. The process is very complicated instead of the comparative simplicity of a S&W. Phil
Northern Virginia Gunworks can do it and it will be as good if not better than Colt's job. they have built my1911 competition pistols and they did a Python for a friend. It is very, very nice. Phil