Aron is a 3rd generation Pokemon that is located in the Glistening Grotto, the cave on the route to Brimber city (4). If you want to get in to the the Glistening Grotto you will need HM06 Rock Smash which can be obtained from beating the Rock Gym in Aredia City. Aron evolves at level 32 to Lairon, and then at level 42 into Aggron. Then you can buy the Mega Stone for it in Anthian city and get mega Aggronite! Have fun with it.