Search the forums for OEM GPS. You'll find what you're looking for.
Most of the GPS receivers we use (like my BU-353) are like a small puck and require no external antenna. They output NMEA-fomatted data, which is merely one "language" of the raw GPS data.
Chances are that sharkfin is merely an antenna that connects to a receiver somewhere else in the car.
The store here sells a Hirschman multi-function antenna that includes a GPS antenna designed to be connected to an OEM-style receiver.