Go to the waterfall at mount cornet then go in the cave.
You can't but the ar code is497816
You can't get the lustrous orb in pokemon diamond but you can in pokemon pearl:after you catch palkia instead of going out keep on going up until you see an item ball witch is a lustrous orb,you can do the same on pokemon diamond but instead you get an adamant orb
I heard this of a page to get a mew if you go to the place where the luster orb is on diamond mew would be there
You cannot get lustrous orb in diamond only platinum or pearl I think.