Hi, Sean. Sand blasters are relatively cheap to buy and beyond that all you need is a big air compressor and the special sand. If you live in a large city, you should be able to contact someone that can do the work easily by checking your phone book. In the smaller towns, you might start by checking with auto parts dealers or auto body repair shops to see if they can do the work or know someone that does.
John2000 is right that there are some people who go overboard when they sand blast. A good commercial shop should give you no problem and might suggest that you glass bead blast. This is safer for your hinges than sand.
If you try to do it yourself, remember that the paint probably has lead in it and you will want to take appropriate precautions.