I am currently teaching Advanced Vocal pedagogy to the pedagogy Masters students at USM. They are certainly keeping me on my toes and I love planning the lectures and assignments. Recently, I asked the students to make a representation of the respiratory system, including the muscles of inhalation and exhalation. They nailed it in such creative ways.
If, however, you would like a super accurate, albeit expensive, model of the abdominal muscles to aid in your explanation of breath support, this model is your best bet!
What I like most about this model is the representation of the transversus abdomens- something most models don't represent yet is an essential part of breath control. It costs around $150 and I feel it is well worth it..