I would ask. Two of my neighbors bring me their grass clippings and leaves for my garden. I just have a certain place by my from fence and they just dump it over. As long as they don't have pesticides or pet waste, I don't see why they would care. Now that I have chickens, my one neighbor brings all his veggie scraps over for them. Works out nicely! You could offer them eggs if you want, but I wouldn't feel obligated to keep them in constant supply as grass is something that they would probably throw away anyway.