Tshirt design for a nonprofit

I work for a small nonprofit that takes scuba trips with disabled veterans. I'd like to get a cool design drawn up for our event attire. I have a concept and general layout -- this trip we are doing rescue diver training. So the design is of a shark who is supposed to be rescuing another shark, but the taco stand shark mistakes it for them ordering tacos. A few specific design elements (the dive flag, red and white striped beach mat, and green emergency oxygen kit) will hopefully tie everything back to our week of training.

I'd like for the design to go on the back of a tshirt. I think a cartoony design would be fun, and I found this attached design inspiration on another tshirt design site (I inquired with them but I had to order a minimum of 50 items -- I only need 17).