I found one near Ladybower Reservoir last year and after a few hours recharging it and trying to get owner info out of it I ended up phoning Garmin with the serial number.

They tracked the owner and gave me a phone number. I phoned the guy who sounded a right miserable git! He'd lost it while mountain biking and sounded like he couldn't care less.

Top and bottom is that I posted it back to him - and he not only never thanked me but didn't offer to refund the postage!

If I found another one I'd do the same tho . . .