I don't know if anyone makes that kind of bra for the G37. However, I hope not. By rubbing and trapping dirt underneath, they will do more harm to your paint than will exposure to the elements and flying road debris.
A much better solution is a so-called "clear" or "invisible" bra. It consists of a sheet of transparent plastic material that is stretched over the nose of the car. Some manufacturers of the material are 3M, DuraShield and DynaShield. A good installer is just as important as the material. Prices range from $150 for a narrow strip above the headlights to $1,000 for covering the entire hood and nose.
There are other threads on this subject. Search for "clear bra" without limiting yourself to the G37 forum. Another place to search for infomation about clear bras is the Porsche Cayman forum,
http://www.caymanclub.net.