You know what, he doesn't have to work because you haven't pushed his responsibilities. He is acting like a spoiled teenager, and getting away with it. Natural consequences would do him a world of good.
You keep getting turned down by agencies you have gone to - haven't they asked what your son's father is providing? Do his parents know that he is such a deadbeat?
Keep the emotion out of it - this is business. And Gabe has a fiscal responsibility to the child he helped bring into the world. I know you don't want to be the one to tell him that he has to grow up - but someone or something has to make an impression on him. He wants Marc to sit in a cell for a few days to get through to him? I think Gabe is the one who needs it more!