It would indeed be fantastic to see a map of the Never Land as imagined by Barrie... Unfortunately, the Barrie archives we have at the hospital date from 1929 when he bequeathed us Peter Pan and the film scenario was written in 1920, so we wouldn't have it. If it still exists, it might well be at the Beinecke Library at Yale, since they have in their collection Barrie's actual film typescript - and different versions of it too. I have seen part of their vast collection but not the map, as I hadn't thought of enquiring about it.
It would be very interesting to know what's happened to it, so if you ever find out, you must let us know.