As one who loves everything about tuna ventresca (belly) except the price, I'm delighted to discover recently cogotes (neck collar cuts). The neck collar has long smooth muscle for a silky texture and is almost as fatty as ventresca with a slightly firmer bite. Agromar brand packed in olive oil is absolutely delicious. And even better, the $5.99 price is about one-third the cost of ventresca.
I bought this at La Espagñola Meats in Harbor City.