That connector is a BNC connector, and is pretty standard to GPS antennas. If you have a few days for delivery
you can probably find a GPS antenna with 3m cable and BNC connector online for $10 or less. Connect that to your GPS and run the cable out a hatch
or port. If it all works then you can start tracking things back and get a proper marine
If you just want to replace the connector on your existing cable then search for a BNC connector, you can probably get one for a couple of bucks at Digi-Key or Mouser (or Radio
Shack if any are still open).