How to get my dog to eat vegan?? urgent?

My husband and i are vegan and recently got a new dog from the humane society. we are very strict vegans and refuse to buy any product that has been associated with the dairy industry or that comes from so that means no leather, eggs etc and obviously no meat. Well we recently got a new dog from the humane society and have been trying to feed him vegan (most dog foods have non-vegan items if not full on meat) and he won't eat ANYTHING. we had some meaty dog food left from a LONG time ago and he ate that up but we refuse to buy anymore. we are worried because we think he might be sick. He seems really hungry and he is getting weak but he won't eat anything we give him. We looked online at vegan dog food but no way do we have money to buy him that. What can we do??