It doesn't exist in Sapphire.
On the way to snow point city.
in snow point city next to the rocks
its not you idiot. its only in Pokemon diamond Pearl and platinum.
You will find it next to the tree by the house on rout 217.before snow point city pick up hm rock climb and then beat snow point city gym
snow point temple in snow point city its at the top of the town map
snowpoint city
You have to transfer from Ruby/Sapphire/Emerald the three Regis, then Regigigas will wake up.
if in the sinnoh region you get it at the snow point city
In snow point city
go to mont corret
break the snowballs
Snow point city