http://lmgtfy.com/?q=gpsunderground
before that though, have you checked with garmin that the seller has notified them of the sale/change of ownership?
also
when you say the unlock code is not working.....each disk has its own unlock code, and you have to load the original CN version onto PC before updating to the latest version, so what i mean is have you got the right code for the version of mapsource you are trying to unlock?
some 2610s were supplied with CN V7, if the seller had upgraded to say CNV9 a separate code should be there for that
I seem to recall that a yellow slip of paper had the code on it as a series of groups of digits and letters....if you didnt get these when you bought the item, why not contact the seller and see if they stored the codes on their PC, as many do!