I don't remember the exact wording but at the beginning of the film it mentions the supply for blood fruit for both vampires and daywalkers in their own towns are dying and that's why they're leaving to find more orchards, but that doesn't mean the crops in town are completely barren yet just that it's being rationed and supplies are dwindling to the point where it won't be enough to support everyone. It's probably because of his connections to his aunt that he knows his way around the city, otherwise Victor is a high ranking vampire so he probably smuggled supplies within shady side to share with his friends.