I had an old MLR GPSr and gave it away to a charity Gav was sending some to. After I sent it I found the Power/Programming lead and a 3 1/2" Floppy with a Windows 95 program for it. I've still got it here.
Not sure if it would be suitable, the GPS connector on the cable resembles the PS2 socket on a computer motherboard but with 8 pin sockets on it and the rectangular locator slightly smaller and rotated 90°.
Any possibility you could e-mail an image of the connector on your gps?