As you are aware , it`s locked because of too many attempts entering the wrong code so the first thing you have to do is obtain the correct code ( Ask here quoting the Serial Number). One possible solution to unlock the radio , is to leave it switched on (undisturbed) for 12 hours or more and hopefully it will reset , allowing you to enter the correct code.
Please post back here whether successful or not.
RegWorts
May 2008