LIDO on Green lanes is good and also cheap. Further up there is a miserable guy in Morrison's arcade.....
The market, in The Mall, in Wood green, I'm sure there's somewhere.
The is a good quality lock smith beside the overground station. They cut good quality keys at a reasonable price.
Sorry to be dense but which Overground ?
Harringay Green Lanes
The one near Wood Green Tube Station which is called Heel Bar according to Google Street View, 198 High Road. Keys cut there always work fine.