I really liked DaylightInventor's design of the sub on Thingiverse, but it was too big to fit in the game's original box. I shrank it down and also used a smaller version of KINGYELLOWJACKET's diver on Thingiverse. For the air marker, I just printed a 10mm sphere.
The sub and scuba divers were all printed in black and painted. You'll want to use supports on the divers, and be careful when removing them. I had to reprint a few because the arms fell off. They might be more sturdy with additional perimeters around the arms.
After finishing, I found ds679's version on Printables. We had the same inspiration, so I listed that as my remix since the other two are on Thingiverse.
The author remixed this model.
Smaller to fit inside the original box, paired with a diver model