Last summer I was after a Garmin
cable at very short notice, albeit for a Satnav (Some "Idiot"
had left the cable for his father's Satnav in a Hire Car!)............to cut a very long story short - I ended up having to order what I needed from Garmin (no one this side of the pond seemed to carry spares - I guess no great demand??). I did so via Mailspeed.
Mailspeed Marine Chandlery
But they may well only be UK folk, but I suspect that any similar Chandlers who carry Garmin as Agents could also easily order anything from Garmin. Took a couple of days from ordering in one of their actual shops to being able to pick up.