That is exactly what I was going to suggest. Hey, you can get livers and gizzards, so why not hearts?Yeah Hare today has it, but 10lbs. is too much and it's not ideal to freeze for months at a time. I'll try local stores and talk to the butcher if they can set them aside for me.
http://feline-nutrition.org/answers/answers-how-much-heart-is-too-muchAside from energy, vitamins and minerals, the heart also contains amino acids, specifically large amounts of taurine. Muscle meat in general contains fairly high amounts of taurine, an amino acid which is necessary for healthy heart and eyes in cats. Generally, the amount of taurine in chicken meat depends on how much work the muscle does, with darker meat indicating harder-working muscles and a higher level of taurine. The heart, being the hardest-working muscle in the body, contains the highest amounts of taurine. In my research, I have not been able to find any evidence that cats can get too much taurine, as any excess is metabolized and excreted in the urine.³