Welcome to UKY. As far as I know, you cannot obtain a passport for your son without his father's consent (i.e. paperwork). This protects children from being taken out of the country against one parent's wishes and is, for the most part, a very good law. Unfortunately, you will have to deal with his fatehr on the paperwork. Do you know anyone who lives in the city where he is? Maybe you could have them bring him the papers, watch him sign them, then forward them on to you. Or, they may be a service you can hire to perform this function for you.
Have you looked at the UKVisa site (ukvisas.gov.uk)? You can probably get most of your information there about the requirements to bring you son over as well as any fees. You may also want to do a search on this site for visa information. There's plenty of information here.
Good luck!