In a large bowl, combine the ground beef, onions, garlic, eggs, Romano cheese, Italian seasoning, salt and pepper. Add the mushrooms to the meat mixture. Slowly stir in the broth, 1/2 cup at a time. The mixture should be very moist but still able to hold its shape when rolled into meatballs. Form the mixture into 2-inch meatballs. Arrange the meatballs in a single layer on a rimmed baking sheet. Bake for 30 to 35 minutes, turning occasionally, until evenly browned.