New, that isn't likely. There are folks out there with New old stock, but that is a needle in the hay stack deal! You are in the right place, I am sure there are 3 or 4 guys parting out GTV6's (As much as it breaks my heart) who can get you a nice used one. Otherwise there is always E-bay.
It's more and likely it's the sending unit in the gear box, or your needle in the speedo bent preventing it from moving. I have a disassembled one I can give you. It's an 85 MPH version. If it's the sending unit no luck! I wish someone could send me one so I can take a crack at fixing it!