Having had to do so for work many times, you can send in GPS units to Garmin for "repair," if the unit is registered on your Garmin account (you can register it right before sending in). Anyway, what they really do is say, oh we don't make that unit anymore and pull back stock from some warehouse and send it to you. You pay something like $100, but that's cheaper than buying a new unit.
That said, these other ideas are way better to just keep the old unit working. Let us know what works.
"Let it ride / Let it roll / Let it go"