There is a
Garmin device that will do this. The NMEA model can be had as an OEM type part pretty inexpensively, i think we got ours from GPSCITY.COM for around $125. You could also mount one of the handheld ones beliw
deck in your nav station where it would also be a secondary display. Some of these will take a cable with
plug and wires for 12v input and NMEA output. I am using an old Garmin GPSmap60 in this way.