If you want a gold chao go and get the stone egg over where you fought choas 0 and go to the shop right next to the place you fought chaos 0 and there shold be in there and pick it up then the doors will close and put the stone egg on the platfrom and leave.

gold
go in the station square area that u fight chaose in at the beginning and by the trees on one side there is a rock pick it up when u walk out of the area with it [past the walls] go left go in the a place that has a green egg pu the rock down and pick the egg up then put the egg down somewher that the egg wasnt before and put the rock where the egg was and then pick the egg up run out and hed 2 chao world then hatch it

4 the silver 1
go 2 the mystic ruins jump in the little pool area and somewhere down there is a little platform on the wall push it in and behind the waterfal high up another one like the one u pushed in will pop out and a silver egg will come out and slowly float 2 the ground pick it up take it 2 chao world and hatch it

and 4 both
i belive u can buy it in the black market